The specification [1] indicates that the tentative used width and height
should be computed first, and if they exceed the `max-width` or
`max-height`, the rules should be applied again using the computed
values of `max-width` and `max-height`.
The only required change to follow the spec is to remove the early
`return` statements, in both `compute_width_for_replaced_element`
and `compute_height_for_replaced_element`.
Fixes#5100.
[1] https://www.w3.org/TR/CSS22/visudet.html#min-max-widths
