Bug 30007: Make ->anonymize methods throw an exception if AnonymousPatron is not set

Bug 30007: Make ->anonymize methods throw an exception if AnonymousPatron is not set

This patch makes the ->anonymize methods throw a
Koha::Exceptions::SysPref::NotSet exception when trying to anonymize
holds and checkouts without AnonymousPatron properly set.

To test:
1. Apply the regression tests patch
2. Run:
   $ kshell
  k$ prove t/db_dependent/Koha/Old/Checkouts.t \
           t/db_dependent/Koha/Old/Holds.t \
           t/db_dependent/Koha/Old/Hold.t
=> FAIL: Tests fail, no exception thrown
3. Apply this patch
4. Repeat 2
=> SUCCESS: Tests pass!
5. Sign off :-D

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
https://bugs.koha-community.org/show_bug.cgi?id=3007
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>