Even if the modules in the given directory never get chosen to be used,
loading arbitrary code from a user-provided directory is not safe when
running as setuid, as the process’ environment comes from an untrusted
source.
Also ignore `GIO_EXTRA_MODULES`.
Spotted by Simon McVittie.
Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
Fixes: #2168