fix: core dumped under Qt 6.4

1. call method metaObject of QMetaType will coredump under Qt 6.4
2. remove `std::terminate()` when AM can't connect to Systemd Signals.
3. call `Subscribe` before connecting to Systemd Signals to guarantee that
   systemd will send UnitNew and UnitRemoved.

Signed-off-by: ComixHe <heyuming@deepin.org>

apps/dde-application-manager/src/main.cpp

@@ -26,6 +26,7 @@ void registerComplexDbusType()
     qDBusRegisterMetaType<QMap<QString, QString>>();
     qRegisterMetaType<PropMap>();
     qDBusRegisterMetaType<PropMap>();
+    qDBusRegisterMetaType<QDBusObjectPath>();
 }
 }  // namespace