Make parsing xml:lang and xml:space infallible
Make parsing xml:lang and xml:space infallible

I.e. make them just log an error if parsing fails.

This is a bit gross; we can refactor it later.

Part-of: <https://gitlab.gnome.org/GNOME/librsvg/-/merge_requests/763>

GNOME/librsvg,GNOME/librsvg,GNOME/librsvg,GNOME/librsvg