Slice threading does not work with hardware acceleration, as decoding
is per-picture. This fixes Bugzilla #542.
Signed-off-by: Diego Biurrun <diego@biurrun.de>
The decoder did not start predicted frames with missing references but
called the end of frame handling on them anyway. This caused an
assertion in the VA API HW accelorator since it tried to render a
picture with uninitialized buffers.