fixes RT #98012, shellcmd STDERR/STDOUT trapping had typo

There's an anti-symmetry in the style of these commands, e.g.

    open(my $oldout, ">&STDOUT") or die $!;
    open(STDOUT, ">&", $oldout)  or die $!;

vs.

    open(OLDERR, ">&", \*STDERR) or die $!;
    open(STDERR, ">&OLDERR")     or die $!;

If you are using a bareword, e.g. STDOUT, then you have to use
`">&STDOUT"` and if you use a variable, e.g. $fh, then you have to use
`">&", $fh`.