Bug 35969: Add error code in opac-sendbasket.pl

Bug 35969: Add error code in opac-sendbasket.pl

No need to carp about empty basket or no reply address.
Just add a simple explanation on the form.

Note that it makes no sense to show the form if the patron
has no email address. We need it as reply-to.

Test plan:
Try opac-sendbasket.pl?bib_list=null
Remove email address from your account, try again.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Emily Lamancusa <emily.lamancusa@montgomerycountymd.gov>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
(cherry picked from commit 35293612a8d0efa932bf376b7855b17cc29d6d5c)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>
(cherry picked from commit 3266b9d5bc80d4aabf47488fff4221d9af516a5e)
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>