Fix for corrupt JPEGs auto-fix PR (#4560)

Auto-fix corrupt JPEGs PR introduced a bug whereby the f.seek() operation read all of the bytes in the image, resulting in the PIL image having nothing to read upon the .save() operation. 

Fix was to re-open the image using PIL before saving.

utils/datasets.py

@@ -873,7 +873,7 @@ def verify_image_label(args):
             with open(im_file, 'rb') as f:
                 f.seek(-2, 2)
                 if f.read() != b'\xff\xd9':  # corrupt JPEG
-                    im.save(im_file, format='JPEG', subsampling=0, quality=100)  # re-save image
+                    Image.open(im_file).save(im_file, format='JPEG', subsampling=0, quality=100)  # re-save image
                     msg = f'{prefix}WARNING: corrupt JPEG restored and saved {im_file}'
 
         # verify labels