Bug 24809: Get only timestamp of deleted items attached to existing bibs when check...

Bug 24809: Get only timestamp of deleted items attached to existing bibs when check if bib deleted

To test:
 1 - Edit/create a file in the koha home dir '/var/lib/koha/{instance}/OAI.yaml' with content like below:
format:
  marcxml:
    metadataPrefix: marcxml
    metadataNamespace: http://www.loc.gov/MARC21/slim http://www.loc.gov/standards/marcxml/schema/MARC21slim
    schema: http://www.loc.gov/MARC21/slim http://www.loc.gov/standards/marcxml/schema/MARC21slim.xsd
    include_items: 1
 2 - Set the systempreferences below to indicated values:
  OAI-PMH => Enable
  OAI-PMH:ConfFile => /var/lib/koha/{instace}/OAI.yaml
 3 - View a record with items and confirm the items show:
  http://localhost:8080/cgi-bin/koha/oai.pl?verb=GetRecord&metadataPrefix=marcxml&identifier=KOHA-OAI-TEST:4
 4 - Delete the items, then delete the record
 5 - Reload the URL from step 3
 6 - Internal Server Error:
  Empty String at /kohadevbox/koha/Koha/OAI/Server/Record.pm line 58.
    at /usr/share/perl/5.24/Carp.pm line 167
 7 - Apply patch
 8 - restart_all
 9 - Repeat
10 - Reload URL from step 3
11 - Success

Signed-off-by: Michal Denar <black23@gmail.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>