avformat/rtsp: check return value of ffurl_read_complete

Signed-off-by: Limin Wang <lance.lmwang@gmail.com>

libavformat/rtsp.c

@@ -1220,7 +1220,8 @@ start:
         content = av_malloc(content_length + 1);
         if (!content)
             return AVERROR(ENOMEM);
-        ffurl_read_complete(rt->rtsp_hd, content, content_length);
+        if (ffurl_read_complete(rt->rtsp_hd, content, content_length) != content_length)
+            return AVERROR(EIO);
         content[content_length] = '\0';
     }
     if (content_ptr)