[gimp/gimp-2-10] app: make sure image colormaps always have at least one color

[Ell <ell src gnome org>]

commit 5e53d06f74b3ad3e807d6bfff7d9854143ca9f73
Author: Ell <ell_se yahoo com>
Date:   Thu Jun 14 03:12:35 2018 -0400

    app: make sure image colormaps always have at least one color
    
    In gimp_image_set_colormap(), make sure the image's colormap always
    has at least one color -- babl palette formats must have at least
    one color.
    
    If the function is called with 0 colors, use black.  We still need
    to support this case, in particular, since existing XCFs may have
    an empty colormap, and since plug-ins can call
    gimp-image-set-colormap with 0 colors.
    
    (cherry picked from commit c16c68e63eded16ec631eed2c0290dfadfaade83)

 app/core/gimpimage-colormap.c | 36 +++++++++++++++---------------------
 1 file changed, 15 insertions(+), 21 deletions(-)
---
diff --git a/app/core/gimpimage-colormap.c b/app/core/gimpimage-colormap.c
index 7a4b1478a0..615e0465d6 100644
--- a/app/core/gimpimage-colormap.c
+++ b/app/core/gimpimage-colormap.c
@@ -182,6 +182,8 @@ gimp_image_set_colormap (GimpImage    *image,
                          gboolean      push_undo)
 {
   GimpImagePrivate *private;
+  GimpPaletteEntry *entry;
+  gint              i;
 
   g_return_if_fail (GIMP_IS_IMAGE (image));
   g_return_if_fail (colormap != NULL || n_colors == 0);
@@ -194,34 +196,26 @@ gimp_image_set_colormap (GimpImage    *image,
 
   if (private->colormap)
     memset (private->colormap, 0, GIMP_IMAGE_COLORMAP_SIZE);
+  else
+    gimp_image_colormap_init (image);
 
   if (colormap)
-    {
-      if (! private->colormap)
-        {
-          gimp_image_colormap_init (image);
-        }
-
-      memcpy (private->colormap, colormap, n_colors * 3);
-    }
-
-  private->n_colors = n_colors;
+    memcpy (private->colormap, colormap, n_colors * 3);
 
-  if (private->palette)
-    {
-      GimpPaletteEntry *entry;
-      gint              i;
+  /* make sure the image's colormap always has at least one color.  when
+   * n_colors == 0, use black.
+   */
+  private->n_colors = MAX (n_colors, 1);
 
-      gimp_data_freeze (GIMP_DATA (private->palette));
+  gimp_data_freeze (GIMP_DATA (private->palette));
 
-      while ((entry = gimp_palette_get_entry (private->palette, 0)))
-        gimp_palette_delete_entry (private->palette, entry);
+  while ((entry = gimp_palette_get_entry (private->palette, 0)))
+    gimp_palette_delete_entry (private->palette, entry);
 
-      for (i = 0; i < private->n_colors; i++)
-        gimp_image_colormap_set_palette_entry (image, i);
+  for (i = 0; i < private->n_colors; i++)
+    gimp_image_colormap_set_palette_entry (image, i);
 
-      gimp_data_thaw (GIMP_DATA (private->palette));
-    }
+  gimp_data_thaw (GIMP_DATA (private->palette));
 
   gimp_image_colormap_changed (image, -1);
 }