do not crash when there are no bookmarks
do not crash when there are no bookmarks

svn path=/trunk/KDE/kdeedu/marble/; revision=1170565

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