Fix parse error when extends from subclass of named classes

(cherry picked from commit ebcfe284751deff4105c68b1d92511ace1a25665)

modules/gdscript/gdscript_parser.cpp

@@ -5238,6 +5238,7 @@ void GDScriptParser::_determine_inheritance(ClassNode *p_class) {
 			if (base_script.is_valid()) {
 
 				String ident = base;
+				Ref<GDScript> find_subclass = base_script;
 
 				for (int i = extend_iter; i < p_class->extends_class.size(); i++) {
 
@@ -5247,7 +5248,7 @@ void GDScriptParser::_determine_inheritance(ClassNode *p_class) {
 
 					if (base_script->get_subclasses().has(subclass)) {
 
-						base_script = base_script->get_subclasses()[subclass];
+						find_subclass = base_script->get_subclasses()[subclass];
 					} else if (base_script->get_constants().has(subclass)) {
 
 						Ref<GDScript> new_base_class = base_script->get_constants()[subclass];
@@ -5255,7 +5256,7 @@ void GDScriptParser::_determine_inheritance(ClassNode *p_class) {
 							_set_error("Constant is not a class: " + ident, p_class->line);
 							return;
 						}
-						base_script = new_base_class;
+						find_subclass = new_base_class;
 					} else {
 
 						_set_error("Could not find subclass: " + ident, p_class->line);
@@ -5263,7 +5264,7 @@ void GDScriptParser::_determine_inheritance(ClassNode *p_class) {
 					}
 				}
 
-				script = base_script;
+				script = find_subclass;
 
 			} else if (!base_class) {