Prevent crash for private types named _ in type_name rules

[sinoru]

Fixes #3971

[SwiftLintBot]

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[codecov-commenter]

Codecov Report

Merging #3972 (3206d1b) into master (ca9217d) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #3972      +/-   ##
==========================================
- Coverage   92.55%   92.55%   -0.01%     
==========================================
  Files         446      446              
  Lines       22490    22490              
==========================================
- Hits        20816    20815       -1     
- Misses       1674     1675       +1     

Impacted Files	Coverage Δ
...ramework/Rules/Idiomatic/GenericTypeNameRule.swift	100.00% <100.00%> (ø)
...ftLintFramework/Rules/Idiomatic/TypeNameRule.swift	95.34% <100.00%> (ø)
...iftLintFramework/Extensions/String+SwiftLint.swift	89.39% <0.00%> (-1.52%)	⬇️

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[SimplyDanny]

Thank you for the bug report and your contribution!

Would you please add a test case that had caused the crash? You can do it like:

Example("...", excludeFromDocumentation: true)

The excludeFromDocumentation keeps the documentation clean and simple.

You may also credit yourself in the CHANGELOG.md.

[SimplyDanny]

Thank you for adding the tests! Now we just have to find the right place for them. 😉