Make logging cost free when there is no output target (#12247)

The logging streams now do almost no work when there is no output target for them.

For example, if LL_VERBOSE has no output targets, then `verbosestream << x` will return a StreamProxy with a null target. Any further `<<` operations applied to it will do nothing.

src/server.cpp

@@ -525,7 +525,7 @@ void Server::start()
 	actionstream << "World at [" << m_path_world << "]" << std::endl;
 	actionstream << "Server for gameid=\"" << m_gamespec.id
 			<< "\" listening on ";
-	m_bind_addr.print(&actionstream);
+	m_bind_addr.print(actionstream);
 	actionstream << "." << std::endl;
 }