If a replaced element has a natural width and a natural height, then the
natural width wins, and the intrinsic height is computed thru the
preferred aspect ratio.
If it has no natural width and no natural height, then the width falls
back to 300px, and again compute the intrinsic height thru the ratio.
However, if it has a natural height but no natural width, then we should
compute the intrinsic width from the natural height thru the ratio. We
were still letting the 300px fallback width win.
Testing: Some tests pass
Fixes: #42573
Signed-off-by: Oriol Brufau <obrufau@igalia.com>