Don't try to write to a buffered socket if there's no data.

This can cause the SSL modules to act weirdly because the TLS
library will return 0 bytes written (correctly) which is then
interpreted as an error.

src/socket_transport.cpp

@@ -42,6 +42,9 @@ bool BufferedSocket::ProcessRead()
 
 bool BufferedSocket::ProcessWrite()
 {
+	if (this->write_buffer.empty())
+		return true;
+
 	int count = this->io->Send(this, this->write_buffer);
 	if (count == 0)
 		return false;