[gimp] Issue #6909: Crash after cancelling out of avif export dialog.

[Jehan <jehanp src gnome org>]

commit 6374481f4fb8c54c8fe9e2db96922f9edb0b6c32
Author: Jehan <jehan girinstud io>
Date:   Sun Sep 26 16:30:29 2021 +0200

    Issue #6909: Crash after cancelling out of avif export dialog.
    
    Do not leave dangling signal handler.

 app/dialogs/file-save-dialog.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)
---
diff --git a/app/dialogs/file-save-dialog.c b/app/dialogs/file-save-dialog.c
index 2bb82bd1bd..69d9260341 100644
--- a/app/dialogs/file-save-dialog.c
+++ b/app/dialogs/file-save-dialog.c
@@ -285,7 +285,12 @@ file_save_dialog_response (GtkWidget *dialog,
         g_free (basename);
 
         if (dialog)
-          gimp_file_dialog_set_sensitive (file_dialog, TRUE);
+          {
+            gimp_file_dialog_set_sensitive (file_dialog, TRUE);
+            g_signal_handlers_disconnect_by_func (dialog,
+                                                  G_CALLBACK (gtk_widget_destroyed),
+                                                  &dialog);
+          }
       }
       break;