avprobe: do not call avio_close() on a custom context

avio_close() can only be called on AVIOContexts created by avio_open(2).

avprobe.c

@@ -1025,7 +1025,8 @@ int main(int argc, char **argv)
     ret = probe_file(input_filename);
     probe_footer();
     avio_flush(probe_out);
-    avio_close(probe_out);
+    av_freep(&probe_out);
+    av_freep(&buffer);
 
     avformat_network_deinit();