[five-or-more] Make MessageDialog modal.

[Arnaud B. <arnaudb src gnome org>]

commit b931650859de079ba2cae92d9eb8850a679e4bd8
Author: Arnaud Bonatti <arnaud bonatti gmail com>
Date:   Thu Aug 6 16:53:53 2020 +0200

    Make MessageDialog modal.

 src/window.vala | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/src/window.vala b/src/window.vala
index 4c2d5ac..fe50338 100644
--- a/src/window.vala
+++ b/src/window.vala
@@ -286,7 +286,7 @@ private class GameWindow : ApplicationWindow
         int n_rows = Game.game_difficulty[size].n_rows;
         int n_cols = Game.game_difficulty[size].n_cols;
         if (game.score > 0 && !game.is_game_over) {
-            var flags = DialogFlags.DESTROY_WITH_PARENT;
+            var flags = DialogFlags.DESTROY_WITH_PARENT | DialogFlags.MODAL;
             var restart_game_dialog = new MessageDialog (this,
                                                          flags,
                                                          MessageType.WARNING,