use br restore point to do PITR from encrypted full backup, Error: proto: BackupMeta: wiretype end group for non-group

## Bug Report

TiDB v8.1

### 1. parameter set

```bash
pd=( --pd http://127.0.0.1:2379 )
key=( --crypter.method aes256-ctr --crypter.key 7878787878787878787878787878787878787878787878787878787878787878 )
fd_log=/db_backup/blog
fd_full=/db_backup/full
```

### 2. backup log nd full ( log start 中可以指定 "`${key[@]}`" 不会出错，但不会生效)

```bash
br log start --task-name test "${pd[@]}" --storage $fd_log
br backup full "${pd[@]}" --storage $fd_full "${key[@]}"
```

### 3. restore point (失败)

```bash
br restore point "${pd[@]}" -s $fd_log --full-backup-storage $fd_full "${key[@]}"
#### Error: proto: BackupMeta: wiretype end group for non-group
```

### 4. restore full + point (成功. restore point 可以指定 "${key[@]}" 不会出错，但不会生效)

```bash
br restore full "${pd[@]}" -s $fd_full "${key[@]}"
br restore point "${pd[@]}" -s $fd_log "${key[@]}" --start-ts xxxxx
```