Optimization: Do not zero-terminate Server::inBuf (#1889)

Optimization: Do not zero-terminate Server::inBuf (#1889)

... when storing unencoded request body bytes in ConnStateData::bodyPipe

Calling SBuf::c_str() is unnecessary in this context because
BodyPipe::append() does not need/expect a zero-terminated buffer. The
call is relatively expensive when the previous Comm::ReadNow() was able
to fill the entire inBuf trailing space, which is a common occurrence
because Server::maybeMakeSpaceAvailable() uses CLIENT_REQ_BUF_SZ as
idealSpace size, and CLIENT_REQ_BUF_SZ is hard-coded to just 4096 bytes.

The call was added in 2014 commit e7287625 that converted inBuf to SBuf.