videorec: Fix flushing encoders
When passing NULL frames, encoders empty their queues, but we have
to stop polling from them when they don't any more data.
#ifndef _SDLname_h_
#define _SDLname_h_
#if defined(__STDC__) || defined(__cplusplus)
#define NeedFunctionPrototypes 1
#endif
#define SDL_NAME(X) SDL_##X
#endif /* _SDLname_h_ */