Bug 30372: Fix value->attribute

Bug 30372: Fix value->attribute

Test plan:
- Activate patron self registration without email verification
- Create several patron attributes as visible and editable in the OPAC, make one mandatory
- Register as a new patron from the OPAC
- Fill in all required fields but the extended attribute
- Fill in at least one of the non-required extended attributes
- Submit
- Verify that the contents of the other extended attribute fields are still present.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
(cherry picked from commit 4616ddc8ab4b7b570f9444f999c2b50a463df6d4)
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
(cherry picked from commit 519aa84d2b6fd5e19bd14dde18d12ba7e10ca06c)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>