nfs: fix bug

I have to mention that this bug is introduced by myself, in the last
commit <fd07f30f> to dfs_nfs.c

components/dfs/filesystems/nfs/dfs_nfs.c

@@ -233,7 +233,7 @@ static nfs_fh3 *get_dir_handle(struct nfs_filesystem *nfs, const char *name)
         copy_handle(handle, &nfs->current_handle);
     }
 
-    while ((file = strtok_r(RT_NULL, "/", &path)) != RT_NULL && path != RT_NULL)
+    while ((file = strtok_r(RT_NULL, "/", &path)) != RT_NULL && path[0] != 0)
     {
         LOOKUP3args args;
         LOOKUP3res res;