lf_hash_iterate() no zero-bucket initialization

Return immediately if hash is empty.

Part of MDEV-20630 - lf_hash get performance regression since the bucket
                     size won't decrease

mysys/lf_hash.c

@@ -522,12 +522,9 @@ int lf_hash_iterate(LF_HASH *hash, LF_PINS *pins,
   CURSOR cursor;
   uint bucket= 0;
   int res;
-  LF_SLIST * volatile *el;
+  LF_SLIST * volatile *el= lf_dynarray_lvalue(&hash->array, bucket);
 
-  el= lf_dynarray_lvalue(&hash->array, bucket);
-  if (unlikely(!el))
-    return 0; /* if there's no bucket==0, the hash is empty */
-  if (*el == NULL && unlikely(initialize_bucket(hash, el, bucket, pins)))
+  if (unlikely(!el) || !*el)
     return 0; /* if there's no bucket==0, the hash is empty */
 
   res= l_find(el, 0, 0, (uchar*)argument, 0, &cursor, pins, action);