UI: Move OBSBasicSettings to scoped block

This ensures that the OBSBasicSettings destructor has been run before
the restart prompt appears, preventing bugs related to OBS shutting down
with the settings window still having active callbacks.

UI/window-basic-main.cpp

@@ -4043,8 +4043,11 @@ void OBSBasic::on_action_Settings_triggered()
 
 	settings_already_executing = true;
 
-	OBSBasicSettings settings(this);
-	settings.exec();
+	{
+		OBSBasicSettings settings(this);
+		settings.exec();
+	}
+
 	SystemTray(false);
 
 	settings_already_executing = false;