cli: fixed cli crash during volume set operation

PROBLEM:

The cli crashes in the following case:
gluster> volume set v3 auth.allow "write-behind"

CAUSE:

The second strncat operation in the last iteration of the for loop,
in cli_to_glusterd writes off the end of the space malloc'd for "cmd",
leading to memory corruption.

FIX:

Made the last strncat operation conditional so that in the last
iteration, strncat is avoided.

Change-Id: I8f836c684f33a6328e384ab8e677b8e32bcb4e55
BUG: 862526
Signed-off-by: Krutika Dhananjay <kdhananj@redhat.com>
Reviewed-on: http://review.gluster.org/4025
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Pranith Kumar Karampuri <pranithk@gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>

cli/src/cli-rpc-ops.c

@@ -6005,7 +6005,8 @@ cli_to_glusterd (gf_cli_req *req, call_frame_t *frame,
 
         for (i = 0; words[i]; i++) {
                 strncat (cmd, words[i], strlen (words[i]));
-                strncat (cmd, " ", strlen (" "));
+                if (words[i+1] != NULL)
+                        strncat (cmd, " ", strlen (" "));
         }
 
         cmd [len - 1] = '\0';