Bug 30318: Don't reset messaging preferences when form is empty

Bug 30318: Don't reset messaging preferences when form is empty

In testing, the messaging preferences are set in the form when EnhancedMessagingPreferences is enabled.
Switching categories silently updates the preferences unless you have made changes, in which case the
user is warned and can confirm if they want to reset or not. The code only applies to patron creatoin, and
does not seem to be taken into account during OPAC self-registration.

It seems the silent defaulting when saving can be removed in favor of the current updates/warns in the actual
form.

To test:
 1 - Set some messaging preferences for at least two categories
 2 - Enter a new patron
 3 - Confirm switching categories correctly defaults the messaging preferences
 4 - Edit the preferences and switch to another category with defaults
 5 - Confirm the warning appears, and preferences are set if confirmed and ignored if not
 6 - Set to a category with defaults, uncheck all, and save
 7 - Ooof, patron is defaulted
 8 - Apply patch
 9 - Repeat 1-5 and confirm nothing has changed
10 - Set to a category with defaults, uncheck all, save
11 - Confirm patron is saved with no preferences

Signed-off-by: Andrew Fuerste Henry <andrewfh@dubcolib.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>