fix: underflow during datetime->nanos conversion

[crepererum]

Fixes #1289.

[codecov]

Codecov Report

Merging #1294 (9b99830) into 0.4.x (3c4846a) will increase coverage by 0.02%.
Report is 3 commits behind head on 0.4.x.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##            0.4.x    #1294      +/-   ##
==========================================
+ Coverage   91.33%   91.35%   +0.02%     
==========================================
  Files          38       38              
  Lines       16971    17034      +63     
==========================================
+ Hits        15501    15562      +61     
- Misses       1470     1472       +2     

Files Changed	Coverage Δ
src/datetime/tests.rs	96.50% <100.00%> (+0.07%)	⬆️
src/naive/datetime/mod.rs	97.39% <100.00%> (+0.04%)	⬆️

... and 2 files with indirect coverage changes

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[djc]

Thanks for the thorough test case!

[pitdicker]

Maybe remove this println!? Or can you change it so that the test compiles on Rust 1.57 (our MSRV)?

[djc]

Just needs println!("nanos: {}", nanos).

[crepererum]

Adjusted the println to be compatible w/ Rust 1.57. I think keeping it helps debugging a failing tests due to the many cases¹.

Footnotes

1. I wish there would be a slightly nicer story for parametrized tests in "standard Rust" though. ↩

[djc]

(Hopefully there will be in the not-too-distant future.)