[gimp] Issue #3070: CRITICAL when converting to Indexed image.

[Jehan <jehanp src gnome org>]

commit 786686a5415526814eb9f7bc004cca591ce3e282
Author: Jehan <jehan girinstud io>
Date:   Wed Jul 17 12:14:10 2019 +0200

    Issue #3070: CRITICAL when converting to Indexed image.
    
    Fixes the GIMP-CRITICAL:
    
    > gimp_babl_format_get_trc: assertion 'format != NULL' failed".
    
    During an indexed conversion, we are in a weird limbo state between the
    time we changed the base-type to GIMP_INDEXED and when we actually set
    the new palette. If during this time, we hit a context switch (which
    typically happens during GUI code; in this specific cases, the various
    progress updates would call gimp_widget_flush_expose() which does
    trigger context switch), then gimp_display_shell_update_title_idle()
    might be idly called. And when it does, it sees an indexed function with
    neither format nor builtin profile.

 app/display/gimpdisplayshell-title.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)
---
diff --git a/app/display/gimpdisplayshell-title.c b/app/display/gimpdisplayshell-title.c
index 6078222f3c..b6cf541dd9 100644
--- a/app/display/gimpdisplayshell-title.c
+++ b/app/display/gimpdisplayshell-title.c
@@ -81,16 +81,28 @@ static gboolean
 gimp_display_shell_update_title_idle (gpointer data)
 {
   GimpDisplayShell *shell = GIMP_DISPLAY_SHELL (data);
+  GimpImage        *image;
 
   shell->title_idle_id = 0;
 
-  if (gimp_display_get_image (shell->display))
+  image = gimp_display_get_image (shell->display);
+  if (image)
     {
       GimpDisplayConfig *config = shell->display->config;
       gchar              title[MAX_TITLE_BUF];
       gchar              status[MAX_TITLE_BUF];
       gint               len;
 
+      /* This is a ugly hack to prevent this function to be called while
+       * an image is being converted to indexed (which may happen as
+       * various context switch happen during progress update). In such
+       * edge case, we end up in an in-between time where the image is
+       * seamingly broken as it has no format (hence no profile either).
+       */
+      if (gimp_image_get_base_type (image) == GIMP_INDEXED &&
+          ! gimp_image_get_layer_format (image, FALSE))
+        return FALSE;
+
       /* format the title */
       len = gimp_display_shell_format_title (shell, title, sizeof (title),
                                              config->image_title_format);