Fixed metadata protokoll corruption on forwarded requests

When forwarding a metadata request through forward_request() we were
adding the required newline char to our buffer, but then sending the
data without it - this results in the forwarded request and the next one
to be garbled together.

Additionally while at it add a warning comment that request string is
not zero terminated anymore after a call to the forward_request()
function - for now this is ok as it is not used by any caller after this.