Fix #2300147 (mistakenly reporting connection error)

* When a mailbox sync is stopped intentionally (for example, if account
  settings change), we report a connection error by mistake
* Handle this case properly, reporting "success" (i.e. no error state)
* Remove obsolete comment

Change-Id: I9bec1244267cd2240c369b9b7f905948381a0f91
1 file changed