Bug 14562: All patrons returned if 1 has a cardnumber set to an empty string (Fix...

Bug 14562: All patrons returned if 1 has a cardnumber set to an empty string (Fix conflict with bug 12833)

This patch is a backport of (Bug 12648 is in 3.20.x, not 3.18.x):
commit 481479fe627dcbabb3ef66df0724cc3fe75b110c
    Bug 12648: Fix conflict with bug 12833

Test plan:
Set the cardnumber of one of the patron to an empty string
Do a patron search and use filters
The search will redirect to the patron detail page of the patron with
the empty string

Signed-off-by: Joonas Kylmälä <j.kylmala@gmail.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Liz Rea <wizzyrea@gmail.com>