Fix stretch when min/max value it outside input data type

[djhoese]

I noticed this while running some tests for my own project. I had a test case (not necessarily based on real-world use cases) where a uint8 array was divided by 500. In main this was converting 500 to the type of the array which was overflowing 500 to the uint8 version of it at 244 which produces unexpected final results.

• Closes #xxxx (remove if there is no corresponding issue, which should only be the case for minor changes)
• Tests added (for all bug fixes or enhancements)
• Tests passed (for all non-documentation changes)
• Passes git diff origin/master **/*py | flake8 --diff (remove if you did not edit any Python files)
• Fully documented (remove if this change should not be visible to users, e.g., if it is an internal clean-up, or if this is part of a larger project that will be documented later)

[codecov]

Codecov Report

Attention: 21 lines in your changes are missing coverage. Please review.

Comparison is base (a84299f) 91.50% compared to head (ba55be6) 91.53%.

Files	Patch %	Lines
trollimage/utilities.py	0.00%	21 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #154      +/-   ##
==========================================
+ Coverage   91.50%   91.53%   +0.02%     
==========================================
  Files          12       12              
  Lines        3969     3970       +1     
==========================================
+ Hits         3632     3634       +2     
+ Misses        337      336       -1     

Flag	Coverage Δ
unittests	91.53% <38.23%> (+0.02%)	⬆️

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[coveralls]

coverage: 91.768% (+0.03%) from 91.74%
when pulling ba55be6 on djhoese:bugfix-stretch-int-overflow
into a84299f on pytroll:main.

[pnuu]

LGTM.

Thanks for fixing the formatting, I didn't realize I hadn't setup pre-commit on my local trollimage repo.

I was thinking that maybe we should create an issue about the reportedly untested functions, but none of them seem to be used in Trollimage.

[djhoese]

Yeah I had no idea these other functions existed that flake8 was complaining about. I think they can be removed but it should probably be done in a separate PR and by someone else.