[gnome-games] preferences-page-platforms-retro-row: Add a translator comment for "None"

[Alexander Mikhaylenko <alexm src gnome org>]

commit 71cf081bff357170f160e0cdd9779aa07d8ffeac
Author: Alexander Mikhaylenko <alexm gnome org>
Date:   Wed Apr 1 22:33:45 2020 +0500

    preferences-page-platforms-retro-row: Add a translator comment for "None"

 src/ui/preferences-page-platforms-retro-row.vala | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/src/ui/preferences-page-platforms-retro-row.vala 
b/src/ui/preferences-page-platforms-retro-row.vala
index 5404bf25..91997eec 100644
--- a/src/ui/preferences-page-platforms-retro-row.vala
+++ b/src/ui/preferences-page-platforms-retro-row.vala
@@ -42,6 +42,7 @@ private class Games.PreferencesPagePlatformsRetroRow : PreferencesPagePlatformsR
                var preferred_core = core_manager.get_preferred_core (platform);
 
                if (preferred_core == null)
+                       /* Translators: No core available for this platform */
                        core_label.label = _("None");
                else {
                        try {
@@ -49,6 +50,7 @@ private class Games.PreferencesPagePlatformsRetroRow : PreferencesPagePlatformsR
                        }
                        catch (Error e) {
                                critical (e.message);
+                               /* Translators: No core available for this platform */
                                core_label.label = _("None");
                        }
                }