when fitted model params are not finite, summary stats blow up

[mitzimorris]

script runPerformanceTests.py parses output of stansummary (I think),
but param values can look like this:

tau[2]          1.0e+201      nan      inf  2.8e+199  2.3e+200  4.5e+201      nan      nan      nan

and the functions which parse this summary (csv_summary and/or parse_summary) blow up.
use math.isfinite to check values before trying to compute average?