Fix a crash on "Switch to Text Diff Editor"

Task-number: QTCREATORBUG-11448

Change-Id: Id0239d5cf71ff857ac384e18136348df92a98b74
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
Qbs: Quieten warning

Quieten warning that is given when accessing a QbsRC before the project
is fully parsed.

Change-Id: I36d52166b4b8c55c85ee5c9d739383c135f1fe58
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>