environment: Set time zero when animations are disabled

environment: Set time zero when animations are disabled

In commit ee09c5c85312f571e14abe69bb6674a361c16d65 we chose to pick
the minimum value in order to preserve 0 instead of replacing it with
1. While returning 0 unconditionally when animations are disabled
seems the more logic thing to do, we were unsure about possible side
effects. Do the change now. Since we are early in the development cycle
we should be able to deal with side effects (if any) on time for the
next release.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2528>