fixed: ticket #10896 - memory leak watching videos with libass subtitles. thanks to evetsso!

(cherry picked from commit 99b4db4d04c9ae35b124e268a29d8c378d94ba10)

git-svn-id: https://xbmc.svn.sourceforge.net/svnroot/xbmc/branches/Dharma@35636 568bbfeb-2a22-0410-94d2-cc84cf5bfa90