Revert "vaapi: return early from ff_vaapi_render_picture() without picture"

This reverts commit 4cbf245f2a2cd2170ca30b0788c2af5b506fe6d6.

I messed up the author information.
vaapi: return early from ff_vaapi_render_picture() without picture

Fixes an assertion when called on uninitialized frame. Spotted after
seeking in vlc.
Fixes ticket #2461.

Tested-by: Timo
Reviewed-by: Joakim Plate
Signed-off-by: Carl Eugen Hoyos <cehoyos@ag.or.at>