[BF] Fix save FODF add header info from i_dwi

[arnaudbore]

Quick description

Using specific data I ended up with different voxels size.

Type of change

Check the relevant options.

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update

Provide data, screenshots, command line to test (if relevant)

...

Checklist

• [x] My code follows the style guidelines of this project (run autopep8)
• [x] I added relevant citations to scripts, modules and functions docstrings and descriptions
• [x] I have performed a self-review of my code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] I moved all functions from the script file (except the argparser and main) to scilpy modules
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 68.79%. Comparing base (1a6818d) to head (9f568b5). Report is 3 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1037 +/- ## ======================================= Coverage 68.79% 68.79% ======================================= Files 432 432 Lines 22456 22456 Branches 3038 3038 ======================================= Hits 15449 15449 Misses 5709 5709 Partials 1298 1298 ``` | [Components](https://app.codecov.io/gh/scilus/scilpy/pull/1037/components?src=pr&el=components&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scilus) | Coverage Δ | | |---|---|---| | [Scripts](https://app.codecov.io/gh/scilus/scilpy/pull/1037/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scilus) | `69.66% <ø> (ø)` | | | [Library](https://app.codecov.io/gh/scilus/scilpy/pull/1037/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scilus) | `67.56% <ø> (ø)` | |