LP#1400376: Don't allow NULL attrs to polute an HSTORE as a key

That causes the HSTORE to blow up, which is bad for circs that
want to succeed.

Signed-off-by: Mike Rylander <mrylander@gmail.com>
Signed-off-by: Ben Shum <bshum@biblio.org>
LP#1400376: Stamping upgrade script for fix to metabib.record_attr

Signed-off-by: Ben Shum <bshum@biblio.org>