avcodec/mediacodecdec: fix immediate EAGAIN with buffered packet

In cases where the mediacodec decoder consumed a partial packet,
receive_frame() would start returning EAGAIN if the rest of the
packet couldn't be flushed and no frames were immediately available.

This fixes receive_frame() to perform its normal blocking wait for
new frames before returning EAGAIN. Fixes an issue I could reproduce
fairly often on a FireOS 6 device, and reported to be happening
intermittently by two mpv users.
Signed-off-by: Aman Gupta <aman@tmm1.net>
Signed-off-by: Matthieu Bouron <matthieu.bouron@gmail.com>

libavcodec/mediacodecdec.c

@@ -452,7 +452,7 @@ static int mediacodec_receive_frame(AVCodecContext *avctx, AVFrame *frame)
 
     /* skip fetching new packet if we still have one buffered */
     if (s->buffered_pkt.size > 0)
-        return AVERROR(EAGAIN);
+        return mediacodec_send_receive(avctx, s, frame, true);
 
     /* fetch new packet or eof */
     ret = ff_decode_get_packet(avctx, &s->buffered_pkt);