Check keywords existing in models.py before checking psr.flags

[mtlam]

I met with a few folks in Europe to try to get our timing (pint_pal) and noise modeling working with simulated libstempo data. However, the simulated tim files lacked the pta and f flags needed in models.py and caused a crash:

enterprise_extensions/enterprise_extensions/models.py

Line 320 in 541dd1f

if ('NANOGrav' in psr.flags['pta'] or 'CHIME' in psr.flags['f']) and not is_wideband:

They were able to fake it out by giving a fake pta flag but also needing a fake f flag. I was going to go in to change these to check for the existence of these flags first in the if statement but checks for 'NANOGrav' in psr.flags['pta'] are throughout the code.

While perhaps less safe, I would recommend writing a helper function somewhere along the lines of

def check_flag(psr, key, value):
    return (key in psr.flags and value in psr.flags[key])

and then replacing the if statements appropriately throughout.