MINOR Fixed Forum_Controller->PostMessageForm() when creating new thread (broken by d58cdbcb)
MINOR Fixed Forum_Controller->PostMessageForm() when creating new thread (broken by d58cdbcb)

Olliepop/silverstripe-forum,mandrew/silverstripe-forum,mandrew/silverstripe-forum,gordonbanderson/silverstripe-forum,camfindlay/silverstripe-forum,camfindlay/silverstripe-forum,Olliepop/silverstripe-forum,gordonbanderson/silverstripe-forum