Don't crash when setting an invalid map theme and the fallback theme does not work either.
Don't crash when setting an invalid map theme and the fallback theme does not work either.

svn path=/trunk/KDE/kdeedu/marble/; revision=1215453

rku/marble,probonopd/marble,adraghici/marble,adraghici/marble,probonopd/marble,tzapzoor/marble,quannt24/marble,David-Gil/marble-dev,quannt24/marble,rku/marble,adraghici/marble,Earthwings/marble,utkuaydin/marble,oberluz/marble,utkuaydin/marble,adraghici/marble,quannt24/marble,tzapzoor/marble,AndreiDuma/marble,tucnak/marble,David-Gil/marble-dev,tucnak/marble,oberluz/marble,AndreiDuma/marble,probonopd/marble,tucnak/marble,David-Gil/marble-dev,tucnak/marble,Earthwings/marble,adraghici/marble,probonopd/marble,quannt24/marble,oberluz/marble,Earthwings/marble,rku/marble,Earthwings/marble,probonopd/marble,utkuaydin/marble,tucnak/marble,tzapzoor/marble,rku/marble,probonopd/marble,utkuaydin/marble,AndreiDuma/marble,tucnak/marble,rku/marble,tzapzoor/marble,adraghici/marble,tzapzoor/marble,AndreiDuma/marble,oberluz/marble,utkuaydin/marble,David-Gil/marble-dev,David-Gil/marble-dev,rku/marble,quannt24/marble,oberluz/marble,Earthwings/marble,quannt24/marble,tucnak/marble,oberluz/marble,Earthwings/marble,utkuaydin/marble,David-Gil/marble-dev,AndreiDuma/marble,probonopd/marble,tzapzoor/marble,AndreiDuma/marble,tzapzoor/marble,tzapzoor/marble,quannt24/marble