Disallow save button if empty name field

Disallow saving game with an empty name field

OpenRA.Mods.Common/Widgets/Logic/GameSaveBrowserLogic.cs

@@ -112,6 +112,7 @@ public GameSaveBrowserLogic(Widget widget, ModData modData, Action onExit, Actio
 				}
 
 				var saveButton = panel.Get<ButtonWidget>("SAVE_BUTTON");
+				saveButton.IsDisabled = () => string.IsNullOrWhiteSpace(saveTextField.Text);
 				saveButton.OnClick = () => { Save(world); };
 				saveButton.IsVisible = () => true;