Merge pull request #67 in ZP/z-push from bugfix/ZP-726-infinit-loop-if-non-stream-given-for-an-attachment to develop

* commit 'ce1fe248':
  ZP-726 Infinit loop if non-stream is given for an attachment. Released under the Affero GNU General Public License (AGPL) version 3. need to check for a resource, as eg. feof("Error") === false and causing infinit loop in while!

(cherry picked from commit aafbbdfa)