Bug 27604: [19.11] Make sure PatronSelfRegistrationLibraryList is used

Bug 27604: [19.11] Make sure PatronSelfRegistrationLibraryList is used

The value of PatronSelfRegistrationLibraryList is used to display the dropdown
list of the libraries, but not after the form is submitted.

Test plan:
1. Empty PatronSelfRegistrationLibraryList
2. Self register a new patron
=> Confirm the dropdown list with the libraries contain all the
libraries
3. Fill in PatronSelfRegistrationLibraryList with branchcodes (eg. "CPL|MPL")
4. Self register a new patron
5. Edit the HTML form and replace the option's value with another
branchcode (FPL)
6. Save
=> Without this patch the branchcode FPL is used
=> With this patch applied an ugly 500 is returned

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
https://bugs.koha-community.org/show_bug.cgi?id=11983

Bug 27604: (QA follow-up) Limit the libraries during the query

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
https://bugs.koha-community.org/show_bug.cgi?id=11983

Bug 27604: Init to {}

Bug 27604: Deal with empty pref

Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>