Handle EPrint::MetaField->ordervalue_single returning undefined

[drn05r]

The following code will throw an error on line 2101 if EPrint::MetaField->ordervalue_single in the for loop pushes an undefined value to the array @r. The value returned should be tested before being push onto the array and only added if defined.

eprints3.4/perl_lib/EPrints/MetaField.pm

Lines 2097 to 2101 in ba25b2d

	foreach( @$value )
	{
	push @r, $self->ordervalue_single( $_ , $session , $langid, $dataset );
	}
	return $session->get_database->quote_ordervalue($self, join( ":", @r ));