Bug 38974: Fix error in OPAC patron update

Test plan:

1) Make sure Patron category is checked in the system preference PatronSelfModificationBorrowerUnwantedField
2) Log in to the opac
3) Go to "Personal details"
4) Select any value for "Date of birth"
5) Click save
6) This must not yield error 500. (But may be a successful save or a validation error).

Signed-off-by: David Nind <david@davidnind.com>

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>

opac/opac-memberentry.pl

@@ -306,6 +306,7 @@ if ( $op eq 'cud-create' ) {
 
     my %borrower = ParseCgiForBorrower($cgi);
     $borrower{borrowernumber} = $borrowernumber;
+    $borrower{categorycode}   = $borrower->{categorycode};
 
     my @empty_mandatory_fields = grep { $_ ne 'password' }    # password is not required when editing personal details
         ( CheckMandatoryFields( \%borrower, $op ), CheckMandatoryAttributes( \%borrower, $attributes ) );