oggenc: remove unneeded null check

The code would have segfaulted before if oggstream were NULL.

CC: libav-stable@libav.org
Bug-Id: CID 732218

libavformat/oggenc.c

@@ -530,7 +530,7 @@ static int ogg_write_header(AVFormatContext *s)
         AVStream *st = s->streams[j];
         OGGStreamContext *oggstream = st->priv_data;
         for (i = 1; i < 3; i++) {
-            if (oggstream && oggstream->header_len[i])
+            if (oggstream->header_len[i])
                 ogg_buffer_data(s, st, oggstream->header[i],
                                 oggstream->header_len[i], 0, 1);
         }