Bug 16082: Display a friendly "patron does not exist" message if that's the case...

Bug 16082: Display a friendly "patron does not exist" message if that's the case - circulation.pl

The major part of pages you can access from a patron detail page (menu)
does not take into consideration the 'patron does not exist' case.
If the borrowernumber is linked to a deleted patron, a friendly message
should be displayed instead of an empty patron detail page.

Test plan:
Go on circ/circulation.pl?borrowernumber=424242
and   circ/circulation.pl?borrowernumber=424242&batch=1
Notice the difference before and after this patch

Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Brendan Gallagher brendan@bywatersolutions.com