fix: use pop() instead of del in process_none_page_numbers

[luojiyin1987]

Bug Description

The process_none_page_numbers function uses del item_copy['page'] which raises KeyError if the 'page' key doesn't exist.

Location

pageindex/page_index.py:677, 681

Problem

item_copy = copy.deepcopy(item)
del item_copy['page']  # KeyError if 'page' doesn't exist

The code assumes 'page' key always exists, but this may not be true for all TOC items.

Impact

• Process crashes with KeyError: 'page'
• Interrupts TOC processing pipeline

Suggested Fix

Use pop() with default value for safe removal:

item_copy.pop('page', None)  # Returns None if key doesn't exist, no error