Issue:
In nameless lookup/other fops, parent inode will be NULL, when we try
to add the cache to the NULL inode, it causes a crash.

Hence handle the scenario of nameless fops, and do not cache/serve
the nameless fops.

>Reviewed-on: https://review.gluster.org/17316
>Smoke: Gluster Build System <jenkins@build.gluster.org>
>NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>
>Reviewed-by: Pranith Kumar Karampuri <pkarampu@redhat.com>
>CentOS-regression: Gluster Build System <jenkins@build.gluster.org>
>(cherry picked from commit 284cd8851bfe60984d2f11b5c52fe3204ff43b06)

Change-Id: I3b90f882ac89e6aaf3419db89e6f890797f37700
BUG: 1454569
Signed-off-by: Poornima G <pgurusid@redhat.com>
Reviewed-on: https://review.gluster.org/17361
NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>
CentOS-regression: Gluster Build System <jenkins@build.gluster.org>
Smoke: Gluster Build System <jenkins@build.gluster.org>
Reviewed-by: Shyamsundar Ranganathan <srangana@redhat.com>