lavf: set is_connected flag so url can be properly closed

Reviewed-by: Lukasz Marek <lukasz.m.luki2 at gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/avio.c

@@ -485,6 +485,7 @@ int avio_open_dir(AVIODirContext **s, const char *url, AVDictionary **options)
     if (ret < 0)
         goto fail;
 
+    h->is_connected = 1;
     ctx->url_context = h;
     *s = ctx;
     return 0;