fill in nNumPrecRadix

Wrongfully removed by commit 808052a13947c9841ce5c9e40860c48bbfbf3434
Date: Tue Jun 20 02:21:13 2006 +0000
which only wanted to make the code warning-free...

But also disallow radix 1 (which does not make much sense)

Change-Id: Id8e313301fa6d5e9643d76865a62cc933999a63e