ResourceLoader: Let resource setup late steps invoke loading in turn

core/io/resource_loader.cpp

@@ -325,7 +325,12 @@ void ResourceLoader::_thread_load_function(void *p_userdata) {
 		MessageQueue::get_singleton()->flush();
 	}
 
+	// We just need to sync with the latest writes. No critical section needed.
+	// As a good side effect, the mutex is unlocked, which is a requirement if
+	// some of the calls below to set the resource up invoke code that in turns
+	// requests resource loading.
 	thread_load_mutex.lock();
+	thread_load_mutex.unlock();
 
 	load_task.resource = res;
 
@@ -389,8 +394,6 @@ void ResourceLoader::_thread_load_function(void *p_userdata) {
 		}
 	}
 
-	thread_load_mutex.unlock();
-
 	if (load_nesting == 0) {
 		if (own_mq_override) {
 			MessageQueue::set_thread_singleton_override(nullptr);