fix the iteration method for external_layout_det_results (#4550)

paddlex/inference/pipelines/seal_recognition/pipeline.py

@@ -259,7 +259,7 @@ class _SealRecognitionPipeline(BasePipeline):
                     layout_det_results = []
                     for _ in doc_preprocessor_images:
                         try:
-                            layout_det_res = list(external_layout_det_results)[0]
+                            layout_det_res = next(external_layout_det_results)
                         except StopIteration:
                             raise ValueError("No more layout det results")
                         layout_det_results.append(layout_det_res)