UI: Don't set theme if it didn't change

If the user just reselects the theme they're already on, we shouldn't
set it again, as setting a theme always introduces issues (that are
especially visible on macOS and Linux).

UI/window-basic-settings.cpp

@@ -3927,7 +3927,8 @@ void OBSBasicSettings::on_theme_activated(int idx)
 {
 	QString currT = ui->theme->itemData(idx).toString();
 
-	App()->SetTheme(currT.toUtf8().constData());
+	if (currT != App()->GetTheme())
+		App()->SetTheme(currT.toUtf8().constData());
 }
 
 void OBSBasicSettings::on_listWidget_itemSelectionChanged()