[FIX] fixed memory leak in DataTransferCollector

There was a TODO ... a TODO that may lead to an OOM error.

Change-Id: I770972a432d108fe8a8d7aa1114e126b2e335dde
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1312
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>