Motivation:

ByteBufferView is not zero indexed, but parseSimpleString assumes it is.

Modifications:

- Correctly compute on the distance between two indices.
- New, somewhat contrived, test case.

Result:

No functional change: because RediStack assumes the remote peer will
always correctly terminate with /r/n, there is no point at which this
code could misbehave in the current implementation. However, with small
changes it is possible to trigger it, as the new test demonstrates.