[libgnome-games-support] Fixed invalid conversion on scores dialog (bgo#794548)

[Robert Roth <robertroth src gnome org>]

commit 1441e37f95ce661805fe5fd17ab1db0ffc89dd5b
Author: Robert Roth <robert roth off gmail com>
Date:   Wed Mar 21 18:42:01 2018 +0200

    Fixed invalid conversion on scores dialog (bgo#794548)

 games/scores/dialog.vala |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/games/scores/dialog.vala b/games/scores/dialog.vala
index 9271f2d..dc6dba5 100644
--- a/games/scores/dialog.vala
+++ b/games/scores/dialog.vala
@@ -300,10 +300,10 @@ private class Dialog : Gtk.Dialog
 
         var name_stack = (Gtk.Stack) grid.get_child_at (2, row_count);
         var widget = name_stack.get_visible_child ();
-        Gtk.Label? user_label = (Gtk.Label) widget;
 
-        if (user_label != null)
+        if (name_stack.get_visible_child_name () == "label")
         {
+            var user_label = (Gtk.Label) widget;
             user_label.set_text (score.user);
         }
         else