quick-read: Do a null check before unref

Backport of http://review.gluster.org/10206

Commit 4ea5b8d2046b9e0bc7f24cdf1b2e72ab8b462c9e seems to have removed the check
as a part of static analyis fixes but I'm seeing errors in the client log.

---------------------
touch  /mnt/fuse_mnt/zero-byte-file
echo 3 > /proc/sys/vm/drop_caches
cat  /mnt/fuse_mnt/zero-byte-file

mount log:
[2015-04-13 05:52:21.683256] E [iobuf.c:790:iobuf_unref] (-->
/usr/local/lib/libglusterfs.so.0(_gf_log_callingfn+0x232)[0x7feda12c0e24] (-->
/usr/local/lib/libglusterfs.so.0(iobuf_unref+0x56)[0x7feda1304c8e] (-->
/usr/local/lib/glusterfs/3.7dev/xlator/performance/quick-read.so(qr_readv_cached+0x466)[0x7fed95b7e2fc]
(-->
/usr/local/lib/glusterfs/3.7dev/xlator/performance/quick-read.so(qr_readv+0x70)[0x7fed95b7e385]
(-->
/usr/local/lib/libglusterfs.so.0(default_readv_resume+0x270)[0x7feda12d4401]
))))) 0-iobuf: invalid argument: iobuf

---------------------

Change-Id: Ia6b29165cdef8783a716fe1e72d3d13bf0220aae
BUG: 1214168
Signed-off-by: Ravishankar N <ravishankar@redhat.com>
Reviewed-on: http://review.gluster.org/10329
Tested-by: NetBSD Build System
Reviewed-by: Raghavendra Talur <rtalur@redhat.com>
Tested-by: Raghavendra Talur <rtalur@redhat.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>

0 files changed, 0 insertions, 0 deletions