[BUGFIX] #5104 Fix e-mail attachments with filenames from memory.

Change-Id: Iea91043dd1899745a84ff6c158de215175f4723d
Reviewed-on: http://review.typo3.org/32487
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>