[gnome-games] preferences-page-platforms-retro-row: Null-check core descriptors

[Alexander Mikhaylenko <alexm src gnome org>]

commit 65fbf2f56d56be5a31dd57d7ad32077bacf02819
Author: Alexander Mikhaylenko <alexm gnome org>
Date:   Sat Sep 12 18:29:56 2020 +0500

    preferences-page-platforms-retro-row: Null-check core descriptors
    
    Fixes criticals when opening preferences.

 src/ui/preferences-page-platforms-retro-row.vala | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/src/ui/preferences-page-platforms-retro-row.vala 
b/src/ui/preferences-page-platforms-retro-row.vala
index a7e985d4..b7ba6c29 100644
--- a/src/ui/preferences-page-platforms-retro-row.vala
+++ b/src/ui/preferences-page-platforms-retro-row.vala
@@ -47,6 +47,9 @@ private class Games.PreferencesPagePlatformsRetroRow : Hdy.ComboRow {
        private void notify_selected_index_cb () {
                var core = model.get_item (selected_index) as Retro.CoreDescriptor;
 
+               if (core == null)
+                       return;
+
                var core_manager = RetroCoreManager.get_instance ();
                core_manager.set_preferred_core (platform, core);
        }