Hopefully fix the random crashes with threads

(cherry picked from commit 13efc1bb06)

core/object.h

@@ -779,8 +779,13 @@ public:
 	static int get_object_count();
 
 	_FORCE_INLINE_ static bool instance_validate(Object *p_ptr) {
+		rw_lock->read_lock();
 
-		return instance_checks.has(p_ptr);
+		bool exists = instance_checks.has(p_ptr);
+
+		rw_lock->read_unlock();
+
+		return exists;
 	}
 };