kohabug 2141 - avoid carp on display of details of deleted bib

kohabug 2141 - avoid carp on display of details of deleted bib

When displaying details of bib in staff interface, check
that bib actually exists and display 404 page if not.  Avoids
following fatal error:

Can't call method "field" on an undefined value at /home/gmc/koha/dev/C4/Biblio.pm line 944.

This situtation can arise when running Zebra; if a bib is deleted,
Zebra will not necessarily be reindexed instantly, allowing a link
from a search result list to point to a missing record.

Signed-off-by: Joshua Ferraro <jmf@liblime.com>