Bug 19366: Do not block patron's detail update if EmailMustBeUnique

Bug 19366: Do not block patron's detail update if EmailMustBeUnique

If the pref PatronSelfRegistrationEmailMustBeUnique is set ("consider"),
a patron is not allowed to register with an existing email address.
The existing code is wrong and reject a patron that is updating their
personal details with "This email address already exists in our
database.", even if the patron did not modify their email address.

This is caused by the query we made, we must search for patron with this
email address but who is not the current patron.

Test plan:
- Set PatronSelfRegistrationEmailMustBeUnique to "consider"
- Register a new patron with an existing email address
=> you should not be allowed
- Use a non-existent email address
=> You should be allowed
- Edit your patron details
- Modify some infos
=> Should pass
- Modify your email address with an existing one
=> You should not be allowed to do that

Followed test plan, patches worked as described
Signed-off-by: Alex Buckley <alexbuckley@catalyst.net.nz>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
(cherry picked from commit ae02cf97e469a17d3bdc9d5c7db702960fd620c8)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>