modify pdf (#7738)

Author: qingzhong1

pipelines/pipelines/nodes/file_converter/pdf.py

@@ -175,6 +175,8 @@ def _read_pdf(self, file_path: Path, layout: bool, process_num: int) -> List[str
         pdf = pypdf.PdfReader(file_path)
         page_length = len(pdf.pages)
         split_len = page_length // process_num
+        if split_len == 0:
+            split_len = page_length
         page_list = [i for i in range(0, page_length, split_len)]
         if page_length > page_list[-1]:
             page_list.append(page_length)