Bug 11282: fix overwriting of existing restrictions when adding new one

Bug 11282: fix overwriting of existing restrictions when adding new one

This patch fixes a bug where using the patron editor to add a new
restriction overwrote the first existing one.

Test Plan:
1) Edit a patron, add a restriction
2) Edit the patron again, add a second restriction
3) Note the first restriction has disappeared!
4) Apply this patch
5) Edit the patron again, add another restriction
6) Note the previous restriction is not longer removed

Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Tested:
- Adding and removing multiple restrictions from
  - the details tab
  - the checkouts tab
  - the edit patron form
All works as expected.
Patch passes all tests in t, xt, and QA script.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>