[gimp] app: fix gimp_pdb_item_is_modifyable() for channels

[Michael Natterer <mitch src gnome org>]

commit a1081bd5956399da6f39301d66df8ea4cafba3fe
Author: Michael Natterer <mitch gimp org>
Date:   Fri Apr 20 19:13:47 2018 +0200

    app: fix gimp_pdb_item_is_modifyable() for channels
    
    When a channel is position-locked, it is also implicitly
    content-locked because we translate channels by modifying their
    pixels.

 app/pdb/gimppdb-utils.c |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)
---
diff --git a/app/pdb/gimppdb-utils.c b/app/pdb/gimppdb-utils.c
index d5f8e34..ecae7ae 100644
--- a/app/pdb/gimppdb-utils.c
+++ b/app/pdb/gimppdb-utils.c
@@ -26,6 +26,7 @@
 
 #include "core/gimp.h"
 #include "core/gimpbrushgenerated.h"
+#include "core/gimpchannel.h"
 #include "core/gimpcontainer.h"
 #include "core/gimpdatafactory.h"
 #include "core/gimpdrawable.h"
@@ -566,6 +567,13 @@ gimp_pdb_item_is_modifyable (GimpItem           *item,
   g_return_val_if_fail (GIMP_IS_ITEM (item), FALSE);
   g_return_val_if_fail (error == NULL || *error == NULL, FALSE);
 
+  /*  When a channel is position-locked, it is also implicitly
+   *  content-locked because we translate channels by modifying their
+   *  pixels.
+   */
+  if ((modify & GIMP_PDB_ITEM_POSITION) && GIMP_IS_CHANNEL (item))
+    modify |= GIMP_PDB_ITEM_CONTENT;
+
   if ((modify & GIMP_PDB_ITEM_CONTENT) && gimp_item_is_content_locked (item))
     {
       g_set_error (error, GIMP_PDB_ERROR, GIMP_PDB_ERROR_INVALID_ARGUMENT,