We null-initialize all of the other pointer members in NewPerSpanData; we should
do the same for these ones, for consistency & robustness.
(In practice, the callers end up initializing these members before reading them
anyway, so it's been benign that we weren't initializing them. But better for
safety & futureproofing to have them reliably initialized.)
https://bugzilla.mozilla.org/show_bug.cgi?id=1547792
Aspect Ratio handling simplified by using floating point integers:
- Multiplication of value (or inverse value) to a known side for Scaling
- No unequal equal values such as "4/3" vs "8/6" vs "20/15"
- Truly "Empty" aspect ratios, even if one dimension is not 0