Ensure mixin class has the attribute

Signed-off-by: Michal Čihař <michal@cihar.com>

weblate/trans/mixins.py

@@ -153,6 +153,7 @@ class PathMixin(LoggerMixin):
     Mixin for path manipulations.
     """
     _dir_path = None
+    _linked_subproject = None
 
     def _get_path(self):
         """
@@ -191,8 +192,7 @@ class PathMixin(LoggerMixin):
                 os.rename(old_path, new_path)
 
             # Clean subproject cache on rename
-            if hasattr(self, '_linked_subproject'):
-                self._linked_subproject = None
+            self._linked_subproject = None
 
     def create_path(self):
         """