[skottie] Fix single-node camera orientation relative to z=0 plane

One-node cameras start off by pointing forward, where "forward" is
decreasing z (as opposed to always facing z==0, as they currently do).

Change-Id: I2ccd5a7cf7d8f0aeeebde1537d44e188aabccd04
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/255117
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>
2 files changed