Add empty list check for element before table to fix "list index out …

…of range"

Signed-off-by: Chris Chase <[email protected]>

src/instructlab/sdg/utils/chunkers.py

@@ -360,7 +360,7 @@ def get_table_page_number(self, json_book, idx):
         """
         prev_page_num, next_page_num = None, None
         for book_element in json_book["main-text"][idx - 1 :: -1]:
-            if "prov" in book_element:
+            if "prov" in book_element and book_element["prov"]:
                 prev_page_num = book_element["prov"][0]["page"]
                 break
         for book_element in json_book["main-text"][idx:]: