Fix: epoch does not increase after finishing warming up

[Haawron]

After the warming up phase, executing scheduler_warmup.step() does not affect scheduler_warmup.last_epoch Since in scheduler_warmup.step, either epoch is None or not, self.after_scheduler.step updates self.after_scheduler.last_epoch instead of self.last_epoch. And it is reasonable to add self.total_epoch + 1 to make epochs seem to be continuing.