Transitions not cancelled

[Rich-Harris]

Haven't fully diagnosed this but it seems maybe the transition manager is behaving as though the initial transition were still in play:

• https://svelte.technology/repl?version=1.55.0&gist=8411165d371374aab0ed259edf1c954e
• https://svelte.technology/repl?version=1.57.1&gist=51c62c40f99041f36f13816049890f94