KDescendantsProxyModel: fix setSourceModel
KDescendantsProxyModel: fix setSourceModel

* disconnect signals should be done on previous sourceModel, not new
* internal data not correct is setSourceModel is done while the source
  model already has some data

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