[gimp] plug-ins: Do not write empty ModelReleaseStatus and DigitalSourceType.

[Jacob Boerema <jboerema src gnome org>]

commit a229454915035628e6d39d6dabc920fec72b66cf
Author: Jacob Boerema <jgboerema gmail com>
Date:   Tue Mar 23 15:19:27 2021 -0400

    plug-ins: Do not write empty ModelReleaseStatus and DigitalSourceType.
    
    Fixes issue #3656 Empty metadata tags are written to XCF at least.
    
    Xmp.plus.ModelReleaseStatus and Xmp.iptcExt.DigitalSourceType are
    defined as combo boxes with a fixed number of possible values.
    However there was no option to leave it empty so there always was
    a value written when saving metadata in the metadata-editor.
    
    We added a "select value" as default option and only write
    metadata if a different value was chosen.
    
    As a bonus we replaced the fixed loop numbers with
    the current actual number of defined choices.

 plug-ins/metadata/metadata-editor.c | 36 ++++++++++++++++++++++++++----------
 plug-ins/metadata/metadata-tags.c   |  2 ++
 2 files changed, 28 insertions(+), 10 deletions(-)
---
diff --git a/plug-ins/metadata/metadata-editor.c b/plug-ins/metadata/metadata-editor.c
index ea15fd9673..6c00078717 100644
--- a/plug-ins/metadata/metadata-editor.c
+++ b/plug-ins/metadata/metadata-editor.c
@@ -1870,7 +1870,7 @@ metadata_dialog_editor_set_metadata (GExiv2Metadata *metadata,
   gtk_combo_box_set_active (GTK_COMBO_BOX (combo_widget), 0);
 
   combo_widget = builder_get_widget (builder, "Xmp.plus.ModelReleaseStatus");
-  for (i = 0; i < 4; i++)
+  for (i = 0; i < n_modelreleasestatus; i++)
     {
       gtk_combo_box_text_append_text (GTK_COMBO_BOX_TEXT (combo_widget),
                                       gettext (modelreleasestatus[i].display));
@@ -1880,7 +1880,7 @@ metadata_dialog_editor_set_metadata (GExiv2Metadata *metadata,
   gtk_widget_set_size_request (combo_widget, 180, height);
 
   combo_widget = builder_get_widget (builder, "Xmp.iptcExt.DigitalSourceType");
-  for (i = 0; i < 5; i++)
+  for (i = 0; i < n_digitalsourcetype; i++)
     {
       gtk_combo_box_text_append_text (GTK_COMBO_BOX_TEXT (combo_widget),
                                       gettext (digitalsourcetype[i].display));
@@ -3545,7 +3545,7 @@ metadata_dialog_editor_set_metadata (GExiv2Metadata *metadata,
                 {
                   gint loop;
 
-                  for (loop = 0; loop < 4; loop++)
+                  for (loop = 0; loop < n_modelreleasestatus; loop++)
                     {
                       if (! strcmp (modelreleasestatus[loop].data, value))
                         {
@@ -3566,7 +3566,7 @@ metadata_dialog_editor_set_metadata (GExiv2Metadata *metadata,
                 {
                   gint loop;
 
-                  for (loop = 0; loop < 5; loop++)
+                  for (loop = 0; loop < n_digitalsourcetype; loop++)
                     {
                       if (! strcmp (digitalsourcetype[loop].data, value))
                         {
@@ -4466,9 +4466,17 @@ metadata_editor_write_callback (GtkWidget  *dialog,
           else if (! strcmp ("Xmp.plus.ModelReleaseStatus",
                              default_metadata_tags[i].tag))
             {
-              gexiv2_metadata_set_tag_string (GEXIV2_METADATA (g_metadata),
-                                              default_metadata_tags[i].tag,
-                                              modelreleasestatus[value].data);
+              if (value == 0)
+                {
+                  gexiv2_metadata_clear_tag (GEXIV2_METADATA (g_metadata),
+                                             default_metadata_tags[i].tag);
+                }
+              else
+                {
+                  gexiv2_metadata_set_tag_string (GEXIV2_METADATA (g_metadata),
+                                                  default_metadata_tags[i].tag,
+                                                  modelreleasestatus[value].data);
+                }
             }
           else if (! strcmp ("Xmp.plus.PropertyReleaseStatus",
                              default_metadata_tags[i].tag))
@@ -4503,9 +4511,17 @@ metadata_editor_write_callback (GtkWidget  *dialog,
           else if (! strcmp ("Xmp.iptcExt.DigitalSourceType",
                              default_metadata_tags[i].tag))
             {
-              gexiv2_metadata_set_tag_string (GEXIV2_METADATA (g_metadata),
-                                              default_metadata_tags[i].tag,
-                                              digitalsourcetype[value].data);
+              if (value == 0)
+                {
+                  gexiv2_metadata_clear_tag (GEXIV2_METADATA (g_metadata),
+                                             default_metadata_tags[i].tag);
+                }
+              else
+                {
+                  gexiv2_metadata_set_tag_string (GEXIV2_METADATA (g_metadata),
+                                                  default_metadata_tags[i].tag,
+                                                  digitalsourcetype[value].data);
+                }
             }
         }
     }
diff --git a/plug-ins/metadata/metadata-tags.c b/plug-ins/metadata/metadata-tags.c
index 9fae102041..7db06de273 100644
--- a/plug-ins/metadata/metadata-tags.c
+++ b/plug-ins/metadata/metadata-tags.c
@@ -166,6 +166,7 @@ const gint n_equivalent_metadata_tags = G_N_ELEMENTS (equivalent_metadata_tags);
  */
 const combobox_str_tag digitalsourcetype[] =
 {
+  { "",                                                              N_("Select a value")                    
               },
   { "http://cv.iptc.org/newscodes/digitalsourcetype/digitalCapture";, N_("Original digital capture of a real 
life scene")    },
   { "http://cv.iptc.org/newscodes/digitalsourcetype/negativeFilm";,   N_("Digitized from a negative on film") 
               },
   { "http://cv.iptc.org/newscodes/digitalsourcetype/positiveFilm";,   N_("Digitized from a positive on film") 
               },
@@ -179,6 +180,7 @@ const gint n_digitalsourcetype = G_N_ELEMENTS (digitalsourcetype);
  */
 const combobox_str_tag modelreleasestatus[] =
 {
+  { "",                                       N_("Select a value")                       },
   { "http://ns.useplus.org/ldf/vocab/MR-NON";, N_("None")                                 },
   { "http://ns.useplus.org/ldf/vocab/MR-NAP";, N_("Not Applicable")                       },
   { "http://ns.useplus.org/ldf/vocab/MR-NAP";, N_("Unlimited Model Releases")             },