player: let explicitly imprecise seeks cancel precise seeks

If an imprecise seek is issues while a precise seek is ongoing,
don't wait up to 300ms (herustistic which usually improves user
experience), but instead let it cancel the seek.

Improves responsiveness of the OSC after the previous commit.

Note that we don't do this on "default-precise" seeks, because we
don't know if they're going to be precise or not.