http_reply(stream) and http_reply(cgi_stream) transfer more data than specified

[triska]

In the final 2 clauses of http_reply_data/4, the goals of the form:

copy_stream(Out, In, Header, 0, end).

should read:

copy_stream(Out, In, Header, 0, Len).

so that only the intended content is actually transmitted.

[JanWielemaker]

It is unclear to me. The last relevant was be200e2, which introduced byte-ranges for files. Before that, the last clauses accepted a length, but did send the
complete stream data. A quick search doesn't really tell me what this is used for and I've forgotten.

Surely, using Len is in general wrong as well, as the input (or output) stream might not be binary. I don't really know what to do with this right now.