Make missing header keywords not cause crashes

[Nat1405]

Files with missing FITS header keywords are causing crashes in Nifty.

I see two possible solutions so far:

• Skip downloads of any files with a "-md!" extension in the gemini archive
• Add robustness to Nifty itself and hope for the best.

Link to example program with affected files: https://archive.gemini.edu/searchform/not_site_monitoring/NotFail/cols=CTOWEQ/GN-2006B-Q-26/notengineering

[Nat1405]

Looks like we can use the Gemini JSON queries to check for these sorts of files.

In GN-2019A-Q-208, N20190303S0069.fits has an -md! extension added. The JSON for it retrieved from this link looks like this for that entry:

   {
        "name": "N20190303S0069.fits",
        "filename": "N20190303S0069.fits.bz2",
        "path": "",
        "compressed": true,
        "file_size": 4104399,
        "data_size": 16807680,
        "file_md5": "7b012638397c33f765b1afd19365cff9",
        "data_md5": "ea80592e78b42ef0e22a84095e464827",
        "lastmod": "2019-12-18 18:02:14.686616+00:00",
        "mdready": false,
        "entrytime": "2019-12-18 18:02:14.707005+00:00",
        "size": 4104399,
        "md5": "7b012638397c33f765b1afd19365cff9",
        "program_id": "GN-2019A-Q-208",
        "engineering": false,
        "science_verification": false,
        "calibration_program": false,
        "observation_id": "GN-2019A-Q-208-101",
        "data_label": "GN-2019A-Q-208-101-001",
        "telescope": "Gemini-North",
        "instrument": "NIFS",
        "ut_datetime": "2019-03-03 07:48:31.900000",
        "local_time": "21:48:31.400000",
        "observation_type": "OBJECT",
        "observation_class": "science",
        "object": "LkHa313B",
        "ra": 86.825960987167,
        "dec": -0.042956990851,
        "azimuth": -115.4491375,
        "elevation": 50.080591666667,
        "cass_rotator_pa": -148.008664871338,
        "airmass": 1.313,
        "filter_name": "INVALID",
        "exposure_time": 250.0,
        "disperser": "J",
        "camera": "NIFS",
        "central_wavelength": 1.25,
        "wavelength_band": "J",
        "focal_plane_mask": "3.0_Mask",
        "detector_binning": "1x1",
        "detector_gain_setting": null,
        "detector_roi_setting": "Fixed",
        "detector_readspeed_setting": null,
        "detector_welldepth_setting": null,
        "detector_readmode_setting": "Medium_Object",
        "spectroscopy": true,
        "mode": "IFS",
        "adaptive_optics": false,
        "laser_guide_star": false,
        "wavefront_sensor": "PWFS2",
        "gcal_lamp": null,
        "raw_iq": 85,
        "raw_cc": 50,
        "raw_wv": 20,
        "raw_bg": 20,
        "requested_iq": 85,
        "requested_cc": 50,
        "requested_wv": 100,
        "requested_bg": 100,
        "qa_state": "Usable",
        "release": "2020-03-03",
        "reduction": "RAW",
        "types": "{'SPECT', 'RAW', 'NIFS', 'IFU', 'SIDEREAL', 'UNPREPARED', 'GEMINI', 'NORTH'}",
        "phot_standard": null
    },

The "mdready" attribute seems to only be false when there's an -md! extension added to the file in the archive.