a panic due to slice out of range

```
panic: runtime error: slice bounds out of range [5:2]

goroutine 1 [running]:
github.com/jackc/chunkreader/v2.(*ChunkReader).Next(0xc0001de400, 0xfffffffffffffffd, 0xc000150000, 0x5, 0x2000, 0x0, 0x0)
/go/pkg/mod/github.com/jackc/chunkreader/v2@v2.0.1/chunkreader.go:61 +0x452
github.com/jackc/pgproto3/v2.(*Frontend).Receive(0xc000555400, 0x5a, 0xc0004f3f00, 0x77, 0x77)
/go/pkg/mod/github.com/jackc/pgproto3/v2@v2.1.1/frontend.go:82 +0x63
github.com/jackc/pgconn.(*PgConn).peekMessage(0xc00083a000, 0x0, 0x0, 0xfffffffe000ce400, 0x0)
/go/pkg/mod/github.com/jackc/pgconn@v1.9.0/pgconn.go:463 +0x346
github.com/jackc/pgconn.(*PgConn).receiveMessage(0xc00083a000, 0xc0000ce400, 0x5a, 0x400, 0x5a)
/go/pkg/mod/github.com/jackc/pgconn@v1.9.0/pgconn.go:485 +0x45
github.com/jackc/pgconn.connect(0x1b08c40, 0xc00004e060, 0xc0008460f0, 0xc000114ba0, 0x0, 0x0, 0x0)
/go/pkg/mod/github.com/jackc/pgconn@v1.9.0/pgconn.go:268 +0x6ee
github.com/jackc/pgconn.ConnectConfig(0x1b08c40, 0xc00004e060, 0xc0008460f0, 0x0, 0x0, 0x0)
/go/pkg/mod/github.com/jackc/pgconn@v1.9.0/pgconn.go:150 +0x2a5
github.com/jackc/pgx/v4.connect(0x1b08c40, 0xc00004e060, 0xc000846000, 0x0, 0x0, 0x406ffa)
/go/pkg/mod/github.com/jackc/pgx/v4@v4.12.0/conn.go:222 +0x16b
github.com/jackc/pgx/v4.ConnectConfig(...)
/go/pkg/mod/github.com/jackc/pgx/v4@v4.12.0/conn.go:113
....
Our redacted stuff
....
main.main()
/go/src/workdir/autogen/cmd/batch-jobs-api-v2-server/main.go:51 +0x4b4
```

It has happened in production during time when the db was not accessible due to maintenance restart, sorry that I do not have more details but this is slice out of bounds you could just check if the index is in length

Start by inspecting chunkreader.go:61 and the call path through pgproto3 Frontend.Receive and pgconn connection setup shown in the stack trace. Reproduce the reported database-unavailable condition if possible, then verify that the connection attempt no longer panics on invalid slice bounds.

Written by the indexing model from the issue text.