Fixes error with generate_fines for overdues returned after closed date

If an overdue is returned after a closed date, the generate_fines code
will not generate fines for those items because the section of code that
checks for closed dates returns from the function if a closed date is
encountered.

For example, if an item is due on June 29th, but is not returned until
after July 1st (Canada Day), then when fines are generated for the item,
generate fines creates a fine for the 30th of June, but when it
gets to the 1st of July it encouters a closed date and executes a
'return' statement which exits the generate_fines code causing the
fine from June 30th to be rolled back as well as preventing
further fines from being generated.

This fix replaces the 'return' statements inside the 'for' loop that is
nested within the eval with 'next' statements.

Signed-off-by: Liam Whalen <whalen.ld@gmail.com>
Signed-off-by: Dan Scott <dscott@laurentian.ca>