Character with byte sequence 0xa2 0xa3 in encoding "EUC_CN" has no equivalent in encoding "UTF8"

## Description

The legacy encodings allow some invalid bytes, which will cause errors
during SELECT operations.

## How to reproduce

```shell
createdb -E EUC_CN -T template0 --locale=C demo_euc_cn_db
```

```sql
demo_euc_cn_db=# CREATE TABLE t(id int, s varchar(10));

demo_euc_cn_db=# INSERT INTO t VALUES(1, E'\xA2\xA3');
INSERT 0 1
demo_euc_cn_db=# SELECT * FROM t WHERE id = 1;
ERROR: character with byte sequence 0xa2 0xa3 in encoding "EUC_CN" has no
equivalent in encoding "UTF8"
```

--
Zhongpu Chen