fixed: crash due to race condition in prompting for skin change after install

(cherry picked from commit 3a808bfe9f37417f36186e600704d22f68ac87b1)

git-svn-id: https://xbmc.svn.sourceforge.net/svnroot/xbmc/branches/Dharma@35571 568bbfeb-2a22-0410-94d2-cc84cf5bfa90