Only checking for the lack of a value in the
checkin_time field causes grocery bills to still
trigger the bill colorizing feature, but because
they have no stop_fines reason they're colored
the same as an overdue item.
This patch requires the presence of a due_date
field before coloring a bill row.
Signed-off-by: Jason Boyer <jboyer@library.in.gov> Signed-off-by: Dan Wells <dbw2@calvin.edu>