pyInterface: Fix another bug in genPseudoData.py.

Fix another bug in genPseudoData which would lead to a crash when a
"artificialy constructed" fit result file was used (i.e. one which did not
contain a flat wave). Also add some printout and fix another error message.

(cherry picked from commit fc286156746e2f7e82bc0cb6758100e8270ab4fb)