gdk/wayland: Make more matched settings from the portal as valid

Commit 97b5fad1 was a forward port from a gtk3 patch, but the hunk was applied on the wrong bits of code.

Ensure the initialization paths also do mark settings read from the portal as valid, so the checks for optional/newer settings actually have the expected result. It is also desirable to mark settings as valid after configuration changes (as that patch did effectively do), but not enough to fix all situations.