NativeScript: Fix initialization in wrong scope

Regression from d702d7b335c0c9305e75131770c0ea739b70d813 which broke javascript build.

modules/gdnative/nativescript/nativescript.cpp

@@ -957,8 +957,8 @@ void NativeScriptLanguage::_unload_stuff(bool p_reload) {
 
 NativeScriptLanguage::NativeScriptLanguage() {
 	NativeScriptLanguage::singleton = this;
-	has_objects_to_register = false;
 #ifndef NO_THREADS
+	has_objects_to_register = false;
 	mutex = Mutex::create();
 #endif
 }