refactor: check conn

src/modules/mpd.cpp

@@ -289,10 +289,13 @@ void waybar::modules::MPD::checkErrors(mpd_connection* conn) {
       state_ = MPD_STATE_UNKNOWN;
       throw std::runtime_error("Connection to MPD closed");
     default:
+      if (conn) {
         auto error_message = mpd_connection_get_error_message(conn);
         mpd_connection_clear_error(conn);
         throw std::runtime_error(std::string(error_message));
       }
+      throw std::runtime_error("Invalid connection");
+  }
 }
 
 void waybar::modules::MPD::fetchState() {