As progress monitors can be triggered from non-UI Threads, make the
StatusLine related methods not fail if called from non-UI Thread.

Change-Id: I5356c86d4944e6d6c96ef3a483cb348f016d421c
Signed-off-by: Mickael Istria <mistria@redhat.com>
Also-By: Andrey Loskutov <loskutov@gmx.de>