Fix NDOF of tracks with no momentum information in PrKalmanFilter
Take into account that number of track parameters is 4 (not 5) for tracks that don't have momentum measurement.
This fixes weird chi2/ndf
peaks for Velo tracks with very small number of hits and relatively large chi2
values, thanks @gunther for spotting this!
Goes with LHCb!4450 (merged)
Edited by Andrii Usachov