Bug 5374 [SIGNED-OFF] Followup: adds conditional check to unit test for late orders

Bug 5374 [SIGNED-OFF] Followup: adds conditional check to unit test for late orders

If there are no late orders in the database, the 5th unit test for C4/Acquisition.pm
fails, since no date is returned (and today's date is expected)

This patch adds a conditional check around whether any late orders are actually returned
by GetLateOrders. If so, tests proceed, if not, they're skipped.  This seems to quiet
the failures in the automated test suite.

http://bugs.koha-community.org/show_bug.cgi?id=5347

signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>