Fix UnboundLocalError when using the predict method with return_predictions=False. (#20484)

* any_on_epoch referenced before assignment

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Luca Antiga <luca.antiga@gmail.com>

Author: 3 people

src/lightning/pytorch/loops/prediction_loop.py

@@ -233,8 +233,9 @@ def _predict_step(
 
         self.batch_progress.increment_ready()
 
-        if not using_dataloader_iter:
-            any_on_epoch = self._store_data_for_prediction_writer(batch_idx, dataloader_idx)
+        any_on_epoch = (
+            self._store_data_for_prediction_writer(batch_idx, dataloader_idx) if not using_dataloader_iter else False
+        )
 
         # the `_step` methods don't take a batch_idx when `dataloader_iter` is used, but all other hooks still do,
         # so we need different kwargs