[FIX] shared file decoration did not update when user left session

This patch ensures that labels are updated properly if a user left the
session.

Change-Id: I222eddc8c2c865bd89f8adf26433dfd0945f3fd6
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1123
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>
Tested-by: Jenkins CI