Make sure to raise the exception for WSGI and make the delete method's intent more clear

data/model/legacy.py

@@ -1235,9 +1235,11 @@ def find_or_create_derived_storage(source, transformation_name, preferred_locati
 def delete_derived_storage_by_uuid(storage_uuid):
   try:
     image_storage = get_storage_by_uuid(storage_uuid)
-    derived_storage = DerivedImageStorage.get(derivative=image_storage)
   except InvalidImageException:
     return
+
+  try:
+    DerivedImageStorage.get(derivative=image_storage)
   except DerivedImageStorage.DoesNotExist:
     return
 

util/queuefile.py

@@ -33,8 +33,8 @@ class QueueFile(object):
         self.raised_exception = True
         for handler in self._exception_handlers:
           handler(result)
-          
-        return
+        
+        raise result
 
       self._buffer += result
       self._total_size += len(result)