commit: simplify code

commit: simplify code

The difference of two unsigned integers is defined to be unsigned, and
therefore it is misleading to check whether it is greater than zero
(instead, the more natural way would be to check whether the difference
is zero or not).

Let's instead avoid the subtraction altogether, and compare the two
operands directly, which makes the code more obvious as a side effect.

Pointed out by CodeQL's rule with the ID
`cpp/unsigned-difference-expression-compared-zero`.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>