Due to some yet-to-be-found bug(s) in intrinsic sizing, we can sometimes
end up deciding that some box has a non-finite intrinsic size.
This will create unpleasant results, and may lead to some layout
algorithms looping infinitely, so this patch adds a safeguard where
we simply turn non-finite intrinsic sizes into zero (and complain a
little bit in the debug log.)
96c9ca502b