opac-user.pl tries to fetch an invalid column when calculating fines.

my $rental_fines = Koha::Account::Lines->search(
    {
        borrowernumber    => $patron->borrowernumber,
        amountoutstanding => { '>' => 0 },
        accounttype       => 'Rent',
        itemnumber        => $issue->{itemnumber}
    },
    {
        select => [ { sum => 'amountoutstanding' } ],
        as     => ['rental_fines']
    }
);
$issue->{rentalfines} = $charges->count ? $charges->next->get_column('rental_fines') : 0;

This code fetches the column "rental_fines" into the variable "$rental_fines", but then tries
to read that column data from a different variable ("$charges").