Downscore per invalid response chunk in single lookup?

[realbigsean]

Description

From @dapplion in #5583

// TODO: We could NOT drop the request here, and penalize the peer again if
// sends multiple penalizable chunks after the first invalid.

If we get an error validating a response in on_single_block_response, currently we drop the request and downscore once, but we could be in the middles of downloading a stream of responses. We wouldn't downscore subsequent invalid responses.