[gimp] app: guard against crash due to quitting while DND is processed

[Nils Philippsen <nphilipp src gnome org>]

commit b1a2c736bf7e6c75ca1af4b4c3330172dddb269e
Author: Nils Philippsen <nils redhat com>
Date:   Fri Jun 10 18:06:02 2011 +0200

    app: guard against crash due to quitting while DND is processed
    
    In gimp_display_shell_drop_uri_list(), shell->display is dereferenced in
    some places without checking that it's still there. It can be set to
    NULL if the user quits the application while a drag and drop action is
    being processed and the main loop is iterated during execution of this
    function. (Bug #652280)

 app/display/gimpdisplayshell-dnd.c |   25 ++++++++++++++++++++++---
 1 files changed, 22 insertions(+), 3 deletions(-)
---
diff --git a/app/display/gimpdisplayshell-dnd.c b/app/display/gimpdisplayshell-dnd.c
index 26cc906..f8e8898 100644
--- a/app/display/gimpdisplayshell-dnd.c
+++ b/app/display/gimpdisplayshell-dnd.c
@@ -479,11 +479,21 @@ gimp_display_shell_drop_uri_list (GtkWidget *widget,
                                   gpointer   data)
 {
   GimpDisplayShell *shell   = GIMP_DISPLAY_SHELL (data);
-  GimpImage        *image   = gimp_display_get_image (shell->display);
-  GimpContext      *context = gimp_get_user_context (shell->display->gimp);
+  GimpImage        *image;
+  GimpContext      *context;
   GList            *list;
   gboolean          open_as_layers;
 
+  /* If the app is already being torn down, shell->display might be NULL here.
+   * Play it safe. */
+  if (! shell->display)
+    {
+      return;
+    }
+
+  image = gimp_display_get_image (shell->display);
+  context = gimp_get_user_context (shell->display->gimp);
+
   GIMP_LOG (DND, NULL);
 
   open_as_layers = (image != NULL);
@@ -495,6 +505,12 @@ gimp_display_shell_drop_uri_list (GtkWidget *widget,
       GError            *error = NULL;
       gboolean           warn  = FALSE;
 
+      if (! shell->display)
+        {
+          /* It seems as if GIMP is being torn down for quitting. Bail out. */
+          return;
+        }
+
       if (open_as_layers)
         {
           GList *new_layers;
@@ -550,7 +566,10 @@ gimp_display_shell_drop_uri_list (GtkWidget *widget,
             warn = TRUE;
         }
 
-      if (warn)
+      /* Something above might have run a few rounds of the main loop. Check
+       * that shell->display is still there, otherwise ignore this as the app
+       * is being torn down for quitting. */
+      if (warn && shell->display)
         {
           gchar *filename = file_utils_uri_display_name (uri);