Follow up for https://github.com/zed-industries/zed/pull/27058 Improves excerpt down button to only scroll when there exists lines more than equal to `expand_excerpt_lines`. This prevents weird shift at end of the file. Before: https://github.com/user-attachments/assets/244a3bd6-d813-4cc8-9dcb-3addba2b652f After: https://github.com/user-attachments/assets/a9a9ba62-a454-4b56-9c8a-d8e6931b270b Release Notes: - N/A