Don't always display the overwrite dialogue

When a save was selected but the filename text was changed,
we don't overwrite the existing save, so we don't need a dialogue

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

@@ -374,7 +374,7 @@ namespace OpenRA.Mods.Common.Widgets.Logic
 				onExit();
 			}
 
-			if (selectedSave != null || File.Exists(testPath))
+			if (File.Exists(testPath))
 			{
 				ConfirmationDialogs.ButtonPrompt(modData,
 					title: OverwriteSaveTitle,