Cast properly for shift operand

`(int) << RHASH_LEV_SHIFT` can be negative integer.

hash.c

@@ -1434,7 +1434,7 @@ hash_iter_lev_inc(VALUE hash)
     }
     else {
         lev += 1;
-        RBASIC(hash)->flags = ((RBASIC(hash)->flags & ~RHASH_LEV_MASK) | (lev << RHASH_LEV_SHIFT));
+        RBASIC(hash)->flags = ((RBASIC(hash)->flags & ~RHASH_LEV_MASK) | ((VALUE)lev << RHASH_LEV_SHIFT));
         if (lev == RHASH_LEV_MAX) {
             iter_lev_in_ivar_set(hash, lev);
         }