asfdemux: Reset number of languages to 0 when freeing the array because of errors

Otherwise we will happily index into the array at NULL if the requested
index is smaller than the number of languages that were previously
allocated.

https://bugzilla.gnome.org/show_bug.cgi?id=777937

gst/asfdemux/gstasfdemux.c

@@ -3962,6 +3962,7 @@ not_enough_data:
     GST_WARNING_OBJECT (demux, "short read parsing language list object!");
     g_free (demux->languages);
     demux->languages = NULL;
+    demux->num_languages = 0;
     return GST_FLOW_OK;         /* not fatal */
   }
 }