do not double sort anymore and don't crash when using an empty document
do not double sort anymore and don't crash when using an empty document

svn path=/branches/work/marble-geodata-nt/marble/; revision=933062

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