fix fetch_column_info function

[oussemabenhassena5]

Root Cause:

The list comprehension inside the max() function generates a list of column widths for items in layout_res where item['category'] == 'sub column'. If there are no items with the 'sub column' category in layout_res, the list will be empty, causing max() to raise the ValueError: max() arg is an empty sequence.

This issue arises only for PDFs where the layout detection does not identify any items with the 'sub column' category. This could happen if:

1. The PDF has a non-standard structure or layout.
2. The model struggles to classify the elements correctly.
3. The detection pipeline filters out all potential 'sub column' items for some reason.