[BUGFIX] #5114 Crash in AbstractMailer in PHP 5.3

Change-Id: I578b884f24bb23d38d67ede09e29f1c0c0fc9d5d
Reviewed-on: http://review.typo3.org/32588
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>