avformat/smoothstreamingenc: removed unused check of avformat_free_context

Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Reviewed-by: Jun Zhao <barryjzhao@tencent.com>
Signed-off-by: Steven Liu <lq@chinaffmpeg.org>

libavformat/smoothstreamingenc.c

@@ -183,8 +183,7 @@ static void ism_free(AVFormatContext *s)
             av_write_trailer(os->ctx);
         if (os->ctx && os->ctx->pb)
             avio_context_free(&os->ctx->pb);
-        if (os->ctx)
-            avformat_free_context(os->ctx);
+        avformat_free_context(os->ctx);
         av_freep(&os->private_str);
         for (j = 0; j < os->nb_fragments; j++)
             av_freep(&os->fragments[j]);