xkbcomp: fix crash when parsing an xkb_geometry section

xkb_geometry sections are ignored; previously the had done so by
returning NULL for the section's XkbFile, however some sections of the
code do not expect this. Instead, create an XkbFile for it, it will
never be processes and discarded later.

Caught with the afl fuzzer.

Signed-off-by: Ran Benita <ran234@gmail.com>
ComputeEffectiveMask(struct xkb_keymap *keymap, struct xkb_mods *mods)
{
    mods->mask = mod_mask_get_effective(keymap, mods->mods);
}

ComputeEffectiveMask(struct xkb_keymap *keymap, struct xkb_mods *mods)
{
    mods->mask = mod_mask_get_effective(keymap, mods->mods);
}
