k2qc crashes on FITS file with missing values for some headers

[JeffLCoughlin]

Running checks on C18, k2qc crashes on a file, which had issues due to missing centroids, and was custom-exported (making this a low-priority issue.) The resulting file is missing values for the following header keywords: RA_OBJ, DEC_OBJ, 1CRVL4, 2CRVL4, 1CRVL5, 2CRVL5, 1CRVL6, 2CRVL6, 1CRVL7, 2CRVL7, 1CRVL8, 2CRVL8, 1CRVL9, 2CRVL9, EXPOSURE, TELAPSE, LIVETIME, TSTART, TSTOP, CRVAL1, CRVAL2

k2qc crashes with the error message:

TypeError: '>' not supported between instances of 'int' and 'Undefined'

Ideally k2qc could gracefully handle the situation and report that the FITS file is missing some keyword values.