bug: The dataset sampler during single GPU training should be infinite

[zizizihua]

In yolox/exp/yolo_base.py:122

if is_distributed:
    batch_size = batch_size // dist.get_world_size()
    sampler = InfiniteSampler(
        len(self.dataset), seed=self.seed if self.seed else 0
    )
else:
    sampler = torch.utils.data.RandomSampler(self.dataset)

torch.utils.data.RandomSampler is not infinite, and will cause exception after an epoch of training.