Fix GlobalWheat2020.yaml auto download (#3007)

ultralytics/datasets/GlobalWheat2020.yaml

@@ -48,7 +48,7 @@ download: |
   # Move
   for p in 'arvalis_1', 'arvalis_2', 'arvalis_3', 'ethz_1', 'rres_1', 'inrae_1', 'usask_1', \
            'utokyo_1', 'utokyo_2', 'nau_1', 'uq_1':
-      (dir / p).rename(dir / 'images' / p)  # move to /images
-      f = (dir / p).with_suffix('.json')  # json file
+      (dir / 'global-wheat-codalab-official' / p).rename(dir / 'images' / p)  # move to /images
+      f = (dir / 'global-wheat-codalab-official' / p).with_suffix('.json')  # json file
       if f.exists():
           f.rename((dir / 'annotations' / p).with_suffix('.json'))  # move to /annotations

ultralytics/yolo/utils/downloads.py

@@ -131,9 +131,10 @@ def safe_download(url,
             a successful download. Default: 1E0.
         progress (bool, optional): Whether to display a progress bar during the download. Default: True.
     """
-    if '://' not in str(url) and Path(url).is_file():  # exists ('://' check required in Windows Python<3.10)
+    f = dir / url2file(url) if dir else Path(file)  # URL converted to filename
+    if '://' not in str(url) and Path(url).is_file():  # URL exists ('://' check required in Windows Python<3.10)
         f = Path(url)  # filename
-    else:  # does not exist
+    elif not f.is_file():  # URL and file do not exist
         assert dir or file, 'dir or file required for download'
         f = dir / url2file(url) if dir else Path(file)
         desc = f'Downloading {clean_url(url)} to {f}'