avcodec/libdav1d: clear the buffered Dav1dData on decoding failure

Should ensure avcodec_send_packet() doesn't return EAGAIN in scenarios where it's not
meant to (e.g., ffmpeg_dec.c where avcodec_receive_frame() is called in a loop to drain
all produced frames before trying to submit more packets).

Fixes ticket #11377.

Reviewed-by: Ronald S. Bultje <rsbultje@gmail.com>
Signed-off-by: James Almer <jamrial@gmail.com>
(cherry picked from commit d1d9b0813a)

libavcodec/libdav1d.c

@@ -372,9 +372,10 @@ static int libdav1d_receive_frame_internal(AVCodecContext *c, Dav1dPicture *p)
 
     res = dav1d_get_picture(dav1d->c, p);
     if (res < 0) {
-        if (res == AVERROR(EINVAL))
+        if (res == AVERROR(EINVAL)) {
+            dav1d_data_unref(data);
             res = AVERROR_INVALIDDATA;
-        else if (res == AVERROR(EAGAIN))
+        } else if (res == AVERROR(EAGAIN))
             res = c->internal->draining ? AVERROR_EOF : 1;
     }