services.simbad: bug-fix cache-reading
services.simbad: bug-fix cache-reading

The tap_query can have more flexible file formatting than imposed by
this `genfromtxt` call. Simply reading the file as a dataframe and
requiring there are rows accomplishes the same, but in a more general
way.

waqasbhatti/astrobase,waqasbhatti/astrobase,lgbouma/astrobase,waqasbhatti/astrobase,lgbouma/astrobase,lgbouma/astrobase