Previously it was being scheduled another time each OnResume, resulting
in more and more calls as a user retries the same beatmap multiple
times.
To simplify things I've decided to just schedule once ever. This means
that on resuming there's no 400ms delay any more, but in testing this
isn't really an issue (load time is still high enough that it will never
really be below that anyway). Even if gameplay was to load faster, the
animation should gracefully proceed.
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