Update _finish_transaction()

Check if the session is ended, and always increment txnNumber.

Author: ajdavis

pymongo/client_session.py

@@ -216,14 +216,17 @@ def abort_transaction(self):
  self._finish_transaction("abortTransaction")
 
  def _finish_transaction(self, command_name):
+ self._check_ended()
+
  if self._current_transaction_opts is None:
  raise InvalidOperation("No transaction started")
 
- if self._server_session.statement_id == 0:
- # Not really started.
- return
-
  try:
+ if self._server_session.statement_id == 0:
+ # Not really started.
+ self._server_session._transaction_id += 1
+ return
+
  # TODO: retryable. And it's weird to pass parse_write_concern_error
  # from outside database.py.
  self._client.admin.command(