ThreadDataLoader can't continuously run

[Nic-Ma]

Describe the bug
Currently, the ThreadDataLoader can only run for 1 epoch, it doesn't contain the reset logic.

Reproduce the issue:

dataset = Dataset(data=self.datalist, transform=self.transform)
dataloader = ThreadDataLoader(dataset=dataset, batch_size=2, num_workers=0)

for d in dataloader:
    self.assertEqual(d["image"][0], "spleen_19.nii.gz")
    self.assertEqual(d["image"][1], "spleen_31.nii.gz")
    self.assertEqual(d["label"][0], "spleen_label_19.nii.gz")
    self.assertEqual(d["label"][1], "spleen_label_31.nii.gz")

for d in dataloader:
    print("will not print here.")

[Nic-Ma]

I will submit a quick PR to fix it ASAP.

Thanks.