avcodec/mediacodecdec: try to receive a frame after signaling EOF to the codec

avcodec/mediacodecdec: try to receive a frame after signaling EOF to the codec

Avoids returning EAGAIN after signaling EOF to the codec in
ff_mediacodec_dec_send() so we can try to receive a frame before
returning in mediacodec_receive_frame().

This helps avoiding an extra round-trip between avcodec_send_frame() and
avcodec_receive_frame() while draining the remaining frames.