Bug 20998: Only perform quicksearch if patron found with cardnumber

Bug 20998: Only perform quicksearch if patron found with cardnumber

This patch makes sure we have a patron before we try to access their
branchcode and allows search to work

To recreate:
1 - Enable 'IndependentBranches'
2 - Setup a patron with all permissions, but not a superlibrarian
3 - Login to staff client as that patron
4 - Click 'Patrons' in the toolbar and try a search
5 - Internal server error
6 - Apply patch
7 - Try the search again
8 - Success!

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>