panic or wrong results when db or index name contains `: ` when reading from `slow_query` table

[time-and-fate]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

Case 1:

use test;
create table t(a int, b int, c int, index `i: a`(a));
insert into t value(1,1,1);
select sleep(1) from t where a = 1;
select index_names from information_schema.slow_query;

Case 2:

create database `a: b`;
use `a: b`;
create table t(a int, b int);
insert into t value ();
select sleep(1) from t;
select * from information_schema.slow_query;

2. What did you expect to see? (Required)

Return correct results.

3. What did you see instead (Required)

Case 1:

+-------------+
| index_names |
+-------------+
|             |
| [t          |
+-------------+

Case 2:

ERROR 1105 (HY000): runtime error: slice bounds out of range [4:3]

4. What is your TiDB version? (Required)

nightly

[Defined2014]

On ad2c9f4 it doesn't panic or get wrong index names anymore. But the database name is empty.