mmal/deinterlace: implement draining of extra pictures in deinterlacer
Fix the source picture was released after turning it into a MMAL_BUFFER_HEADER_T. Not sure how this could work. The while loop to create output picture is turned into single calls. One in the filter function and others in the drain calls. The assert done before returning a valid picture is moved up in the Filter callback. We no longer return pictures chained using vlc_picture_chain_AppendChain().