[ticket/12356] Assign vars preventing Plupload from loading in PM editor.

PHPBB3-12356
Merge remote-tracking branch 'prototech/ticket/12356' into develop-ascraeus

* prototech/ticket/12356:
  [ticket/12356] Assign vars preventing Plupload from loading in PM editor.
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [ticket/12356] Assign vars preventing Plupload from loading in PM editor.