Chunker not returning chunks on pdf's with only header sections.

### Bug
When a pdf is so simple that it seemingly only contains two headers the hybrid chunker is not returning any chunks.
Even so the export_to_markdown function returns a result.

### Steps to reproduce
https://colab.research.google.com/drive/15yDYj501f-W3ro55Nv1UfP_R-P5TrIxU?usp=sharing

### Docling version
Version: 2.52.0

### Python version
3.12.11 (main, Jun 4 2025, 08:56:18) [GCC 11.4.0]

The pdf in question. Also included in the colab.
[broken_pdf.pdf](https://github.com/user-attachments/files/22297499/broken_pdf.pdf)