fix MongoEngine#153 and bump version

Author: rochacbruno

flask_mongoengine/operation_tracker.py

@@ -138,7 +138,7 @@ def _remove(collection_self, spec_or_id, safe=None, **kwargs):
 def _cursor_refresh(cursor_self):
     # Look up __ private instance variables
     def privar(name):
-        return getattr(cursor_self, '_Cursor__{0}'.format(name))
+        return getattr(cursor_self, '_Cursor__{0}'.format(name), None)
 
     if privar('id') is not None:
         # getMore not query - move on

setup.py

@@ -24,7 +24,7 @@
 
 setup(
     name='quokka-flask-mongoengine',
-    version='0.7.3',
+    version='0.7.4',
     url='https://github.com/mongoengine/flask-mongoengine',
     license='BSD',
     author='Ross Lawley',