Revert "avcodec/bsf: Forbid packet without payload in av_bsf_send_packet"

This reverts commit bfdca87ab55c7f69087d962dc47aa45c8c6436fb.

Packets with no data or side data will be valid EOF signal in an
upcoming merge.

Signed-off-by: James Almer <jamrial@gmail.com>
