Let repeating model animation run before start time

[lilleyse]

Fixes #3932

[pjcozzi]

The code snippet in #3932 seems to work OK in master: http://cesium-dev.s3-website-us-east-1.amazonaws.com/cesium/master/Apps/Sandcastle/index.html?src=Hello%20World.html&label=Showcases

[pjcozzi]

Doesn't work in master when ran locally, but works in this branch.

[pjcozzi]

Looking in the debugger, I see your changes in the hosted version. I suspect there is a bug in CI where it deploys the most recent branch to master's directory (or some branch since this is not the most recently updated one).

[pjcozzi]

Update CHANGES.md in master.

[pjcozzi]

I suspect there is a bug in CI where it deploys the most recent branch to master's directory (or some branch since this is not the most recently updated one)

Actually, the other branches could just be failing CI, but they should also be deployed, but perhaps just not overwriting master.