Bug 11693: Default emailing preferences not loaded for self registering patron

Bug 11693: Default emailing preferences not loaded for self registering patron

The call to AddMember_Opac does not take care of the messaging prefs
when enhanced messaging is enabled.
This patch adds the call to handle_form_action to do that.

Test plan:
Enable self registering patrons and enhanced messaging.
Check the (default) message prefs for the relevant patron category. At least
enable email for one notice.
Self-register a user with and without verification email enabled.
Check in both cases that the message prefs of the user conform to
those in the patron category. (So at least one enabled.)

Followed test plan, works as expected.
Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
(cherry picked from commit f7ed250d618c57a3fc00728bbb93460b25ceda52)
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>