Fix thread checking to queue instances for deletion

modules/mono/mono_gd/gd_mono.cpp

@@ -705,7 +705,7 @@ bool _GodotSharp::is_domain_loaded() {
 
 void _GodotSharp::queue_dispose(Object *p_object) {
 
-	if (Thread::get_main_id() == Thread::get_caller_id() && !GDMono::get_singleton()->is_finalizing_scripts_domain()) {
+	if (GDMonoUtils::is_main_thread() && !GDMono::get_singleton()->is_finalizing_scripts_domain()) {
 		_dispose_object(p_object);
 	} else {
 #ifndef NO_THREADS
@@ -722,7 +722,7 @@ void _GodotSharp::queue_dispose(Object *p_object) {
 
 void _GodotSharp::queue_dispose(NodePath *p_node_path) {
 
-	if (Thread::get_main_id() == Thread::get_caller_id() && !GDMono::get_singleton()->is_finalizing_scripts_domain()) {
+	if (GDMonoUtils::is_main_thread() && !GDMono::get_singleton()->is_finalizing_scripts_domain()) {
 		memdelete(p_node_path);
 	} else {
 #ifndef NO_THREADS
@@ -739,7 +739,7 @@ void _GodotSharp::queue_dispose(NodePath *p_node_path) {
 
 void _GodotSharp::queue_dispose(RID *p_rid) {
 
-	if (Thread::get_main_id() == Thread::get_caller_id() && !GDMono::get_singleton()->is_finalizing_scripts_domain()) {
+	if (GDMonoUtils::is_main_thread() && !GDMono::get_singleton()->is_finalizing_scripts_domain()) {
 		memdelete(p_rid);
 	} else {
 #ifndef NO_THREADS

modules/mono/mono_gd/gd_mono_utils.h

@@ -149,6 +149,10 @@ void attach_current_thread();
 void detach_current_thread();
 MonoThread *get_current_thread();
 
+_FORCE_INLINE_ bool is_main_thread() {
+	return mono_domain_get() != NULL && mono_thread_get_main() == mono_thread_current();
+}
+
 GDMonoClass *get_object_class(MonoObject *p_object);
 GDMonoClass *type_get_proxy_class(const StringName &p_type);
 GDMonoClass *get_class_native_base(GDMonoClass *p_class);