xdg-open fails on file: urls with query strings

Attempting to open a file:/// url with a query string fails because it tries to check if the file exists including the query string.

This bug was reported and fixed previously, but seems to have regressed. See here: https://bugs.freedesktop.org/show_bug.cgi?id=45857 and fix here: 5913207e. It looks like the whole file was rewritten since then, so it was not easy to figure out where to re-do the change.