LibProtocol: Keep reading until an error occurs for buffered reads

When buffering is enabled for the entire protocol request, it's possible
that the entirety of the file data might be available on the first read
of the pipe passed from RequestServer. If the file is then closed on the
RequestServer end, the client would never realize that the file is EOF
and call the user-provided on_finish callback.

By reading until there's an error, we expect to get an EAGAIN or similar
non-blocking pipe error message if there is still more data.

Userland/Libraries/LibProtocol/Request.cpp

@@ -69,7 +69,6 @@ void Request::stream_into(Stream& stream)
                 break;
             // FIXME: What do we do if this fails?
             stream.write_until_depleted(read_bytes).release_value_but_fixme_should_propagate_errors();
-            break;
         } while (true);
 
         if (m_internal_stream_data->read_stream->is_eof())