avformat/http: Fix off by 1 error

Fixes: out of array access
Fixes: zeropath/off-by-one-one-byte

Found-by: Joshua Rogers <joshua@joshua.hu>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/http.c

@@ -1875,7 +1875,7 @@ static int store_icy(URLContext *h, int size)
             ret = http_read_stream_all(h, data, len);
             if (ret < 0)
                 return ret;
-            data[len + 1] = 0;
+            data[len] = 0;
             if ((ret = av_opt_set(s, "icy_metadata_packet", data, 0)) < 0)
                 return ret;
             update_metadata(h, data);