index name is not saved correctly.

[siddontang]

create table t (c1 int, c2 int, index(c1), index(c2);
insert into values (1, 2), (3,4);
select * from t where c1 > 0;

it will output:

+----+----+
| c1 | c2 |
+----+----+
| 1  | 2  |
| 1  | 2  |
| 3  | 4  |
| 3  | 4  |
+----+----+

This is not correct. And we find that both c1 and c2 index use the same empty index name.