FcSolveSolver: cleanup ressources

Summary:
The FcSolveSolver did not call its free function in patsolve, leading to
ressource exhaustion.

Fixes: BUG-395624

Reviewers: #kde_games, shlomif, wbauer, aacid

Reviewed By: wbauer, aacid

Subscribers: fuksitter, wbauer, kde-games-devel

Differential Revision: https://phabricator.kde.org/D23570