Fix mkdocs.yml raw image URLs (#14213)

Signed-off-by: Glenn Jocher <glenn.jocher@ultralytics.com>
Co-authored-by: UltralyticsAssistant <web@ultralytics.com>
Co-authored-by: Burhan <62214284+Burhan-Q@users.noreply.github.com>

ultralytics/nn/tasks.py

@@ -276,7 +276,7 @@ class BaseModel(nn.Module):
             batch (dict): Batch to compute loss on
             preds (torch.Tensor | List[torch.Tensor]): Predictions.
         """
-        if not hasattr(self, "criterion"):
+        if getattr(self, "criterion", None) is None:
             self.criterion = self.init_criterion()
 
         preds = self.forward(batch["img"]) if preds is None else preds