[Bug] Bookmark export doesn't truncate file on overwriting

[danpla]

Describe the bug

When the bookmarks export overwrites an existing HTML file larger than the exported one, the resulting file is not truncated, that is, it contains trailing data from the original file, and its size stays the same.

How to Reproduce

1. Add some bookmarks to DDG and export them.
2. Delete half of the bookmarks and export them again to the same file, confirming overwriting.
3. Observe the size and contents of the file.

Expected behavior

It should truncate/delete the overwritten file on export.

Environment

- DDG App Version: 5.156
- Device: Armor X7
- OS: Android 10