gfapi : check the value "iovec" in glfs_io_async_cbk only for read

The glfs_io_async_cbk() is called from the cbk of all the async ops
such as write, read, fsync, ftruncate. In all other cases, expect for
read the value for "iovec" is NULL. From the code, glfs_io_async_cbk
checks the value in common routine which may end up in failures.

Thanks Joe Julian for finding issue and suggesting the fix.

Cherry picked from commit 61d72b3d91f2655b04de4ef29262f738a8cf7369:
> Change-Id: I0be0123da68f9d8fbb5d94ede2d45566a9add6a5
> BUG: 1349276
> Signed-off-by: Jiffin Tony Thottan <jthottan@redhat.com>
> Reported-by: Joe Julian <me@joejulian.name>
> Reviewed-on: http://review.gluster.org/14779
> Reviewed-by: Niels de Vos <ndevos@redhat.com>
> Smoke: Gluster Build System <jenkins@build.gluster.org>
> Tested-by: Kaleb KEITHLEY <kkeithle@redhat.com>
> NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>
> CentOS-regression: Gluster Build System <jenkins@build.gluster.org>
> Reviewed-by: Joe Julian <me@joejulian.name>

Change-Id: I0be0123da68f9d8fbb5d94ede2d45566a9add6a5
BUG: 1350880
Reported-by: Joe Julian <me@joejulian.name>
Signed-off-by: Niels de Vos <ndevos@redhat.com>
Reviewed-on: http://review.gluster.org/14822
Smoke: Gluster Build System <jenkins@build.gluster.org>
NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>
Reviewed-by: Kaleb KEITHLEY <kkeithle@redhat.com>
CentOS-regression: Gluster Build System <jenkins@build.gluster.org>
Reviewed-by: jiffin tony Thottan <jthottan@redhat.com>

0 files changed, 0 insertions, 0 deletions