Remove the temp file if it is empty after the request has failed

Remove the temp file if it is empty after the request has failed

After using cg-update to pull, empty files named *.temp are left in
the various subdirectories of .git/objects/.  These are created by
git-http-fetch to hold data as it's being fetched from the remote
repository.  They are left behind after a transfer error so that the
next time git-http-fetch runs it can pick up where it left off.  If
they're empty though, it would make more sense to delete them rather
than leaving them behind for the next attempt.

Signed-off-by: Nick Hengeveld <nickh@reactrix.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>