[mutter] monitor-config-migration: Discard if configured mode is missing

[Jonas Ådahl <jadahl src gnome org>]

commit 43eeb009ce78588db9fba48574f377629d5de1aa
Author: Jonas Ådahl <jadahl gmail com>
Date:   Mon Sep 25 17:57:18 2017 -0400

    monitor-config-migration: Discard if configured mode is missing
    
    If a configuration key matched a current system state, but no monitor
    mode was found (for example because of an incorrect refresh rate),
    discard it while logging a warning.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=787668

 src/backends/meta-monitor-config-migration.c |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)
---
diff --git a/src/backends/meta-monitor-config-migration.c b/src/backends/meta-monitor-config-migration.c
index c862168..d619dc4 100644
--- a/src/backends/meta-monitor-config-migration.c
+++ b/src/backends/meta-monitor-config-migration.c
@@ -1208,6 +1208,13 @@ meta_finish_monitors_config_migration (MetaMonitorManager *monitor_manager,
       monitor_mode_spec = monitor_config->mode_spec;
       monitor_mode = meta_monitor_get_mode_from_spec (monitor,
                                                       monitor_mode_spec);
+      if (!monitor_mode)
+        {
+          g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED,
+                       "Mode not available on monitor");
+          return FALSE;
+        }
+
       scale = meta_monitor_calculate_mode_scale (monitor, monitor_mode);
 
       logical_monitor_config->scale = scale;