[gnome-control-center/gnome-3-32] display: Add guards for NULL display configuration

[Benjamin Berg <bberg src gnome org>]

commit 5a6ff6ad76db415cb3f5defd264e569e11a7dde4
Author: Benjamin Berg <bberg redhat com>
Date:   Wed Jul 3 09:53:38 2019 +0200

    display: Add guards for NULL display configuration
    
    This may happen under some conditions. Possibly due to a race condition
    (i.e. we did not receive any configuration from mutter yet) or also if
    we are not running on GNOME.
    
    Add guards for NULL configuration. This configuration is never
    applicable and mostly clears the UI.
    
    Fixes: #604
    (cherry picked from commit 345a819f84853ec331e7ae2f522a046cca96951a)

 panels/display/cc-display-panel.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)
---
diff --git a/panels/display/cc-display-panel.c b/panels/display/cc-display-panel.c
index 7970e8654..65ee587c5 100644
--- a/panels/display/cc-display-panel.c
+++ b/panels/display/cc-display-panel.c
@@ -721,6 +721,12 @@ rebuild_ui (CcDisplayPanel *panel)
   g_list_store_remove_all (panel->primary_display_list);
   gtk_list_store_clear (panel->output_selection_list);
 
+  if (!panel->current_config)
+    {
+      panel->rebuilding_counter--;
+      return;
+    }
+
   n_active_outputs = 0;
   n_usable_outputs = 0;
   outputs = cc_display_config_get_ui_sorted_monitors (panel->current_config);
@@ -962,6 +968,12 @@ update_apply_button (CcDisplayPanel *panel)
   gboolean config_equal;
   g_autoptr(CcDisplayConfig) applied_config = NULL;
 
+  if (!panel->current_config)
+    {
+      reset_titlebar (panel);
+      return;
+    }
+
   applied_config = cc_display_config_manager_get_current (panel->manager);
 
   config_equal = cc_display_config_equal (panel->current_config,