features/index: closedir() if fd_ctx_set() fails in __index_fd_ctx_get.

Change-Id: I9ab599cf4a90c2e285d63ec0f56af210709285b6
BUG: 1166284
Signed-off-by: Vijay Bellur <vbellur@redhat.com>
Reviewed-on: http://review.gluster.org/9168
Reviewed-by: Venky Shankar <vshankar@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Pranith Kumar Karampuri <pkarampu@redhat.com>
Tested-by: Pranith Kumar Karampuri <pkarampu@redhat.com>