Avoid schedule frames if GstVideoOverly is used
Avoid schedule frames if GstVideoOverly is used

When GstVideoOverly is used there is no appsink, playing of a frame is
done according the time value of its buffer

Acked-by: Frediano Ziglio <55d48b080b2e443e395cde84d2c83b135a4ff48e@redhat.com>

flexVDI/spice-gtk,flexVDI/spice-gtk