animationUtils: Skip no-op wiggle to avoid cancelling pending transitions

animationUtils: Skip no-op wiggle to avoid cancelling pending transitions

When wiggle() is called with duration 0, the async easeAsync calls
yield between microtasks, leaving pending operations that remove
transitions on the same property. This becomes a problem when two
setMessage() calls happen in the same call stack (e.g. via
_queuePriorityMessage): the first fires a no-op wiggle(dur:0) and
the second starts the real wiggle(dur:65). When microtasks drain,
the first wiggle's pending easeAsync calls overwrite the second
wiggle's active transition, effectively cancelling the real animation.

Return early when duration is 0, since the animation is a no-op anyway.

Fixes: fdadbb7a5a2 ("animationUtils: Use easeAsync() for wiggle")
Closes: https://gitlab.gnome.org/GNOME/gnome-shell/-/work_items/9207
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/4209>