Fixes crash, when removing last torrent.BUG: 388803

Summary: Torrent wasn't removed from queuemanager properly. Thus calling the data(..) function caused ktorrent to crash.

Test Plan:

1. Have one completed torrent in ktorrent
2. Remove this torrent
3. Ktorrent doesnot crash anymore

Reviewers: stikonas, trufanov

Reviewed By: stikonas

Differential Revision: https://phabricator.kde.org/D25680