vorbisenc: add missing parenthesis

Bug-Id: CID 1238791

libavcodec/vorbisenc.c

@@ -1091,11 +1091,12 @@ static int vorbis_encode_frame(AVCodecContext *avctx, AVPacket *avpkt,
     avpkt->size = put_bits_count(&pb) >> 3;
 
     avpkt->duration = ff_samples_to_time_base(avctx, avctx->frame_size);
-    if (frame)
+    if (frame) {
         if (frame->pts != AV_NOPTS_VALUE)
             avpkt->pts = ff_samples_to_time_base(avctx, frame->pts);
-    else
+    } else {
         avpkt->pts = venc->next_pts;
+    }
     if (avpkt->pts != AV_NOPTS_VALUE)
         venc->next_pts = avpkt->pts + avpkt->duration;