pipeline: post message with an invalid clock.
gst_pipeline_change_state
should do gst_object_ref(clock)
before gst_message_new_new_clock
because there is a gst_object_unref(clock)
coming after it.
gst_pipeline_change_state
should do gst_object_ref(clock)
before gst_message_new_new_clock
because there is a gst_object_unref(clock)
coming after it.