adjustment: sanity-check values when setting them

adjustment: sanity-check values when setting them

It's not enough to sanitize values when starting an animation, as the
adjustment can reconfigure itself while the animation runs.
So as a simple way to handle this, we sanitize every value right before
setting it, too.

In the future we might also want to look at sanitizing start/end values
of the animation.

Fixes #5763