suzerain: #3073 fix diter=0 and/or siter=0

Previously, specifying these wouldn't cause any solve at all
contrary to the method documentation.

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@44358 0bd85f0b-c151-43b9-a1e9-27231104551f