PropertyEditor: Add missing MAKE_PROPSELECT.

Fixes #15745

editor/property_editor.cpp

@@ -665,6 +665,8 @@ bool CustomPropertyEditor::edit(Object *p_owner, const String &p_name, Variant::
 
 			} else if (hint == PROPERTY_HINT_PROPERTY_OF_INSTANCE) {
 
+				MAKE_PROPSELECT
+
 				Object *instance = ObjectDB::get_instance(hint_text.to_int64());
 				if (instance)
 					property_select->select_property_from_instance(instance, v);