LibIPC+Services: Make ClientConnection take socket as NonnullRefPtr

This avoids getting into the awkward situation where the socket is
still part-owned by main() in multi-instance service. Also it just
reads nicer.

Services/WebContent/main.cpp

@@ -54,6 +54,7 @@ int main(int, char**)
     }
 
     auto socket = Core::LocalSocket::take_over_accepted_socket_from_system_server();
-    IPC::new_client_connection<WebContent::ClientConnection>(*socket, 1);
+    ASSERT(socket);
+    IPC::new_client_connection<WebContent::ClientConnection>(socket.release_nonnull(), 1);
     return event_loop.exec();
 }