rewrite tricky loop to avoid -Wsizeof-array-div
rewrite tricky loop to avoid -Wsizeof-array-div

I don't see anything particularly wrong with the code as written, but
it's triggering a warning from the new Clang -Wsizeof-array-div because
it _looks_ like a bug, dividing sizeof(SkPoint[2]) by sizeof(SkScalar).
(The answer is 4.)

We can rewrite this to just not trigger the warning.

See https://bugs.fuchsia.dev/p/fuchsia/issues/detail?id=36439

Bug: fuchsia:36439
Change-Id: I73bef83add9050d95b3ccf69e613ab009c6a152b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/240825
Auto-Submit: Mike Klein <14574f09dfa9b4e14759b88c3426a495a0e627b0@google.com>
Commit-Queue: Brian Salomon <61fabaaf0876044aeedfd8e351e485c028d69e7b@google.com>
Reviewed-by: Brian Salomon <61fabaaf0876044aeedfd8e351e485c028d69e7b@google.com>

HalCanary/skia-hc,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,google/skia,aosp-mirror/platform_external_skia,google/skia,HalCanary/skia-hc,google/skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,HalCanary/skia-hc,HalCanary/skia-hc,HalCanary/skia-hc,HalCanary/skia-hc,HalCanary/skia-hc,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,HalCanary/skia-hc,google/skia,aosp-mirror/platform_external_skia,HalCanary/skia-hc,HalCanary/skia-hc,google/skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia