Bug 10227 : Fix GetMessagingPreferences when digest is possible

Bug 10227 : Fix GetMessagingPreferences when digest is possible

This bug is a bit tricky to test, as the result is somehow  random, depending on the order of rows returned by sql request. You've got to change the preferences several times to see bad results.

Enable EnhancedMessaging preferences
Set preferences for a borrower or a category.
run misc/cronjobs/advance_notices.pl and look in message_queue table the letter_code of the generated messages.
Change digest selection and do the test again several times

Without patch, for message where digest is allowed (Advance_Notice, Item_Due), for a borrower or a category with 'wants_digest' selected, GetBorrowerMessagingPreferences returns sometimes letter_code with DGST and sometimes not.

With the patch, letter_code returned is always correct depending on digest selected or not

Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>