Fix exposure slider

[Vincent-Stragier]

Description

Find the closest exposure value to avoid the slider jumping to the left.

Fixes #47

Type of change

• [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

How Has This Been Tested?

Tested locally.

Tested on the following devices:

• [ ] Development environment (Linux, Windows, or MacOS)
• [x] Pi Zero 2 W
• [ ] Pi Zero W
• [ ] Pi 3A+
• [ ] Pi 3B+
• [x] Pi 4

Checklist:

• [ ] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [x] My changes generate no new warnings
• [x] New and existing unit tests pass locally with my changes

[mikevanis]

Nice one, thank you for yet another contribution!

[Vincent-Stragier]

@mikevanis, happy to help ;-)