Use real current file format when importing

We need to use real class instead of the base class. The
AutoFormat.parse can return different class which will then better
understand the file format.
Signed-off-by: Michal Čihař <michal@cihar.com>

weblate/trans/models/translation.py

@@ -1099,7 +1099,7 @@ class Translation(models.Model, URLMixin, PercentMixin, LoggerMixin):
         # Load backend file
         try:
             # First try using own loader
-            store = self.subproject.file_format_cls.parse(
+            store = self.store.parse(
                 StringIOMode(fileobj.name, filecopy),
                 self.subproject.template_store
             )