The return value from xread() is ssize_t.
Paolo Teti <paolo.teti@gmail.com> pointed out that in this case, the
signed return value was assigned to an unsigned type (size_t). This patch
fixes that.
Signed-off-by: Johan Herland <johan@herland.net> Signed-off-by: Junio C Hamano <junkio@cox.net>