git-commit.sh: Fix usage checks regarding paths given when they do not make sense

git-commit.sh: Fix usage checks regarding paths given when they do not make sense

The checks that looked for paths given to git-commit in addition to
--all or --interactive expected only 3 values, while the case statement
actually provides 4, so the check was never triggered.

The bug was introduced in 6cbf07efc5702351897dee4742525c9b9f7828ac when
the case statement was extended to handle --interactive.

Signed-off-by: Björn Steinbrink <B.Steinbrink@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>