Bug 16204: Show friendly error message if trying to edit record which no longer exists

Bug 16204: Show friendly error message if trying to edit record which no longer exists

To test:
1) Create a record
2) Click Edit -> Edit record. open this in another tab
3) Delete the record in the original tab
4) Refresh the edit form in the other tab. Notice the software error
5) Apply patch and refresh page
6) There should be a nice error message with the form fields and buttons
hidden. Confirm links work as expected.

Sponsored-by: Catalyst IT
Signed-off-by: Claire Gravely <claire.gravely@bsz-bw.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>