sha1_name: don't waste cycles in the @-parsing loop
sha1_name: don't waste cycles in the @-parsing loop

The @-parsing loop unnecessarily checks for the sequence "@{" from
(len - 2) unnecessarily.  We can safely check from (len - 4).

Signed-off-by: Ramkumar Ramachandra <5c355d1d38066ed0c5de420d67c1b5ed0687c4bd@gmail.com>
Signed-off-by: Felipe Contreras <de77a8b9cd239b204c19c52ed62e48ab47243362@gmail.com>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git