avformat/oggenc: don't flush twice when the last packet is side data only

Commit 18f24527eb accidentally made side data only packets be handled like a
flush request. Fix this regression by effectively ignoring them as was the
original intention.

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

libavformat/oggenc.c

@@ -687,8 +687,8 @@ static int ogg_write_packet(AVFormatContext *s, AVPacket *pkt)
 {
     int i;
 
-    if (pkt && pkt->size)
-        return ogg_write_packet_internal(s, pkt);
+    if (pkt)
+        return pkt->size ? ogg_write_packet_internal(s, pkt) : 0;
 
     for (i = 0; i < s->nb_streams; i++) {
         OGGStreamContext *oggstream = s->streams[i]->priv_data;

tests/ref/lavf/ogg

@@ -1,3 +1,3 @@
-507a906a705d16f3a3b0c4114c738110 *tests/data/lavf/lavf.ogg
+81b9366cacb23644c2803585dced9996 *tests/data/lavf/lavf.ogg
 13516 tests/data/lavf/lavf.ogg
 tests/data/lavf/lavf.ogg CRC=0x3a1da17e