timedated: do not incorrectly close non-opened dbus connection

timedated: do not incorrectly close non-opened dbus connection

Fix the fallowing error when no system dbus available:

Failed to get system D-Bus connection: Failed to connect to socket /var/run/dbus/system_bus_socket: No such file or directory
process 14920: arguments to dbus_connection_close() were incorrect, assertion "connection != NULL" failed in file ../../dbus/dbus-connection.c line 2889.
This is normally a bug in some application using the D-Bus library.
process 14920: arguments to dbus_connection_unref() were incorrect, assertion "connection != NULL" failed in file ../../dbus/dbus-connection.c line 2776.
This is normally a bug in some application using the D-Bus library.