Protect against maskedconstant return from gaia query of no RV

[wbalmer]

I went ahead and tested the case where the host star requested has no RV measurement in Gaia DR3. To test this, I tried initializing backtracks.System with target_name='Kepler-1900'. The previous try/except loop let this past without raising the Except, I think because the Gaia.query_object_async table for a star with no RV actually gives a numpy.ma.core.MaskedConstant object in the radial_velocity column.

There was also a FutureWarning raised when trying to print this maskedconstant using format strings, so I added a if/else to protect against that, should numpy change this behavior in the future.

Creating a PR because I'm not sure if changing this try/except statement so dramatically leaves System.init unprotected to other exceptions Gilles was thinking of.

[gotten]

Thanks for testing what actually comes back from the Gaia query. The double try except was because I didn't know yet what the query returned. If it was not an integer or float I would throw an exception and if it was something that would break the code I would also throw an exception. So we only need one exception now :).

Go ahead and merge this fix.

There might still be 3 debug lines in the code, do you need them?:

              print(type(self.radvelo))
               print(type(target_gaia['radial_velocity'][0]))
               print(isinstance(self.radvelo, (int, float)))

[wbalmer]

Ah, let me remove my debug prints, thanks for catching them!