fix treatment of B=0 track extrapolation X estimates
fix treatment of B=0 track extrapolation X estimates

miranov25/AliRoot,alisw/AliRoot,shahor02/AliRoot,coppedis/AliRoot,miranov25/AliRoot,shahor02/AliRoot,coppedis/AliRoot,coppedis/AliRoot,shahor02/AliRoot,alisw/AliRoot,miranov25/AliRoot,alisw/AliRoot,coppedis/AliRoot,coppedis/AliRoot,shahor02/AliRoot,alisw/AliRoot,alisw/AliRoot,alisw/AliRoot,shahor02/AliRoot,miranov25/AliRoot,coppedis/AliRoot,miranov25/AliRoot,miranov25/AliRoot,alisw/AliRoot,coppedis/AliRoot,shahor02/AliRoot,coppedis/AliRoot,miranov25/AliRoot,shahor02/AliRoot,miranov25/AliRoot,alisw/AliRoot