[skottie] Clamp OpacityEffect values

Animated opacities can yield values > 1, which trigger RenderContext
asserts.

Clamp explicitly to avoid this issue.  Also avoid allocating a new
RenderContext when the value is >= 1 (no op).

TBR=
Change-Id: I1639af7ab50f4ccf9cd79cb950f14b64dd2619ba
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/408256
Reviewed-by: Florin Malita <fmalita@google.com>
Commit-Queue: Florin Malita <fmalita@google.com>
1 file changed