Bug 38288: Fallback to Standard if FreeForm

A regular openURL works fine:
http://localhost:8080/cgi-bin/koha/opac-illrequests.pl?backend=Standard&title=Koha%20is%20cool&method=create&genre=article&openurl=1

Problem is existing third-party systems may be linking to Koha using FreeForm, not Standard

Test plan:
1) Access the OPAC URL from above.
2) Notice it works.
3) Replace the word 'Standard' with 'FreeForm'. It no longer works.
4) Apply patch. Repeat.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>

opac/opac-illrequests.pl

@@ -117,6 +117,7 @@ if ( $op eq 'list' ) {
             backends    => $req->available_backends
         );
     } else {
+        $params->{backend} = 'Standard' if $params->{backend} eq 'FreeForm';
         my $request = Koha::ILL::Request->new
             ->load_backend($params->{backend});