[gnome-flashback] monitor-config: free `meta_monitor_spec` safely

[Alberts Muktupāvels <muktupavels src gnome org>]

commit 18eb4e75dddc370dc61090c257a8f36c0d1bcca1
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Sun Jan 31 15:25:15 2021 +0200

    monitor-config: free `meta_monitor_spec` safely
    
    Based on mutter commit:
    https://gitlab.gnome.org/GNOME/mutter/-/commit/88647ae23cd818c28f

 backends/gf-monitor-config.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
---
diff --git a/backends/gf-monitor-config.c b/backends/gf-monitor-config.c
index aaeda8b..a8f0968 100644
--- a/backends/gf-monitor-config.c
+++ b/backends/gf-monitor-config.c
@@ -48,7 +48,9 @@ gf_monitor_config_new (GfMonitor     *monitor,
 void
 gf_monitor_config_free (GfMonitorConfig *config)
 {
-  gf_monitor_spec_free (config->monitor_spec);
+  if (config->monitor_spec != NULL)
+    gf_monitor_spec_free (config->monitor_spec);
+
   g_free (config->mode_spec);
   g_free (config);
 }