Saves checkpoint at first iteration of feature extractor (#363)

# Description

Saves a checkpoint file on the first iteration of the feature extractor
so that a checkpoint is available if inferencing early on in the
training process. Previously, we had to wait until 50k steps for the
checkpoint to be saved.

## Type of change

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applicable. -->

- Bug fix (non-breaking change which fixes an issue)


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## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.sh --format`
- [x] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] I have updated the changelog and the corresponding version in the
extension's `config/extension.toml` file
- [ ] I have added my name to the `CONTRIBUTORS.md` or my name already
exists there

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source/isaaclab_tasks/isaaclab_tasks/direct/shadow_hand/feature_extractor.py

@@ -175,14 +175,14 @@ class FeatureExtractor:
                     pose_loss.backward()
                     self.optimizer.step()
 
-                    self.step_count += 1
-
                     if self.step_count % 50000 == 0:
                         torch.save(
                             self.feature_extractor.state_dict(),
                             os.path.join(self.log_dir, f"cnn_{self.step_count}_{pose_loss.detach().cpu().numpy()}.pth"),
                         )
 
+                    self.step_count += 1
+
                     return pose_loss, predicted_pose
         else:
             img_input = torch.cat((rgb_img, depth_img, segmentation_img), dim=-1)