fix #H9312 - partly eaten food in bones shop

fix #H9312 - partly eaten food in bones shop

Dying in a shop while carrying partly eaten food would place that food
on the floor without marking it no_charge.  But marking it that way
wouldn't have helped because as bones data gets saved, every object on
the level has its no_charge flag cleared.  So 'no_charge' needs to be
explicitly set for partly eaten food in tended shops as a bones level
gets loaded.

Most of the shk.c diff is reformatting, but it does change the
get_pricing_units() routine to lie that the quantity is zero for
partly eaten food so that when multiplying with price it won't matter
whether the price has been forced to zero or been left non-zero.