Flush remaining messages before quitting the game when loading fails

This change allows error messages to be printed in the editor debugger when the game fails on load, instead of displaying them in the console terminal only.

main/main.cpp

@@ -2090,6 +2090,11 @@ void Main::cleanup() {
 
 	ERR_FAIL_COND(!_start_success);
 
+	if (script_debugger) {
+		// Flush any remaining messages
+		script_debugger->idle_poll();
+	}
+
 	ResourceLoader::remove_custom_loaders();
 	ResourceSaver::remove_custom_savers();