ultralytics 8.0.72 faster Windows trainings and corrupt cache fix (#1912)

Co-authored-by: andreaswimmer <53872150+andreaswimmer@users.noreply.github.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

ultralytics/yolo/data/dataset.py

@@ -77,7 +77,6 @@ class YOLODataset(BaseDataset):
         nm, nf, ne, nc, msgs = 0, 0, 0, 0, []  # number missing, found, empty, corrupt, messages
         desc = f'{self.prefix}Scanning {path.parent / path.stem}...'
         total = len(self.im_files)
-        nc = len(self.data['names'])
         nkpt, ndim = self.data.get('kpt_shape', (0, 0))
         if self.use_keypoints and (nkpt <= 0 or ndim not in (2, 3)):
             raise ValueError("'kpt_shape' in data.yaml missing or incorrect. Should be a list with [number of "