Remove special-case of "0" in niceSort

Since now niceSort is more consistently behaved, we don't have the
special casing. This should have been removed in commit a7f0953a, but
I didn't realise it.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>