common: Use iobuf_get_noeof to avoid undefined behaviors.

common: Use iobuf_get_noeof to avoid undefined behaviors.

* common/iobuf.c (block_filter): Use iobuf_get_noeof.

--

Cherry-pick from master commit of:
	f80346f42df4bdc7d0a9741c3922129aceae4f81

When signed integer has negative value, left shift computation is
undefined in C.

GnuPG-bug-id: 4093
Reported-by: Philippe Antoine
Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>
(cherry picked from commit 0383e7fed7b2a45c7f0ae4c11415c6a9a3a3ddb7)

Gbp-Pq: Name common-Use-iobuf_get_noeof-to-avoid-undefined-behaviors.patch