In editor contexts, the `StartTimeBindable` subscription in `HitObject`
was firing before defaults were applied, which in the case of sliders
manifested in an infinite end time. `ApplyDefaults()` also did not
always set the time of the control point to the correct value, which
matters when the beatmap is encoded.
Ensure that the control points receive the correct time values during
default application, and only register the `StartTimeBindable` change
callback after defaults have been successfully applied.
7a25fe79b7