imsim.py crashes if there are no stars in the instance catalog

[jchiang87]

The problem is that when phoSimStarCatalog.get_fitsFiles() is called, there are no objects to be simulated and no bandPassDict is created because of
https://github.com/lsst/sims_GalSimInterface/blob/master/python/lsst/sims/GalSimInterface/galSimCatalogs.py#L358
and this line in imsim.py
https://github.com/LSSTDESC/imSim/blob/master/bin.src/imsim.py#L153
fails with

Traceback (most recent call last):
  File "/gpfs/slac/kipac/fs1/g/desc/imsim_deep/imSim/bin/imsim.py", line 179, in <module>
    main()
  File "/gpfs/slac/kipac/fs1/g/desc/imsim_deep/imSim/bin/imsim.py", line 165, in main
    phoSimGalaxyCatalog.copyGalSimInterpreter(phoSimStarCatalog)
  File "/gpfs/slac/kipac/fs1/g/desc/imsim_deep/PRs/sims_GalSimInterface/python/lsst/sims/GalSimInterface/galSimCatalogs.py", line 429, in copyGalSimInterpreter
    self.bandpassDict = otherCatalog.bandpassDict
AttributeError: 'ImSimStars' object has no attribute 'bandpassDict'

[danielsf]

We can probably fix this by putting

if otherCatalog.hasBeenInitialized:
    self.bandpassDict = otherCatalog.bandpassDict
    self.galSimInterpreter = otherCatalog.galSimInterpreter

here
https://github.com/lsst/sims_GalSimInterface/blob/master/python/lsst/sims/GalSimInterface/galSimCatalogs.py#L418

Then, the first catalog that contains objects will initialize the GalSimInterpreter

[danielsf]

Do you want me to deal with this, or have you already done something?

[jchiang87]

Let's hold off for now. There may be other related issues that come up as I go through my testing for the PRs.

[danielsf]

OK

[jchiang87]

@danielsf I just tried your proposed fix, and it worked fine, so I'm ok with proceeding this way.

[danielsf]

Okay. I will just add it to the existing GalSimInterface PR

[danielsf]

I just merged the sims_GalSimInterface PR, including the fix to this bug.