check for errors during preprocessing, not after

nnunetv2/preprocessing/preprocessors/default_preprocessor.py

@@ -252,6 +252,7 @@ def run(self, dataset_name_or_id: Union[int, str], configuration_name: str, plan
                                            'reducing the number of workers might help')
                     done = [i for i in remaining if r[i].ready()]
                     for _ in done:
+                        r[_].get()  # allows triggering errors
                         pbar.update()
                     remaining = [i for i in remaining if i not in done]
                     sleep(0.1)