Fix bug where visible, but unlit areas of the target body were not mapped

[ortk95]

Corrected bug where the mapping routine used the illuminated rather than visible flag when determining which parts of the target's surface need mapping, potentially leading to some visible parts of the surface being unmapped.

Closes #377

Pull request checklist

• [x] Add a clear description of the change
• [x] Add any new tests needed
• [x] Run spell check on new text visible to user (documentation, GUI etc.)
• [x] Check any changes to requirements.txt are reflected in setup.py and conda-forge feedstock
• [x] Check code passes CI checks (run run_ci.sh or check GitHub Actions)

See CONTRIBUTING.md for more details.

[coveralls]

Pull Request Test Coverage Report for Build 9713180923

Details

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 99.611%

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Totals
Change from base Build 9711575616:	0.0%
Covered Lines:	3105
Relevant Lines:	3117

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💛 - Coveralls