RedundantStringChars is unsafe for autocorrection when string is too short or empty

[corsonknowles]

phone_number.number.chars[0..9] autocorrected to: phone_number.number[0..9].chars This will raise when number[0..9] is blank.

Instead, it should be autocorrected to: phone_number.number[0..9]&.chars

We have a similar nil handling problem when the string is too short instead of blank:

irb(main):001> twenty_character_string = "twenty_character_string"
=> "twenty_character_string"
irb(main):002> twenty_character_string[40..80].chars
(irb):2:in `<main>': undefined method `chars' for nil (NoMethodError)

twenty_character_string[40..80].chars
                               ^^^^^^

So the safe operator will make this safe.

---

Expected behavior

Expected autocorrect result to not raise error undefined methodchars' for nil (NoMethodError)` for example by using a safe operator.

Actual behavior

Safe Autocorrect will create code that raises errors, either when the string is too short or when it's entirely empty (e.g. with a variable that can be blank or have a string of any length).

Steps to reproduce the problem

irb(main):001> twenty_character_string = "twenty_character_string"
=> "twenty_character_string"
irb(main):002> twenty_character_string[40..80].chars
(irb):2:in `<main>': undefined method `chars' for nil (NoMethodError)

twenty_character_string[40..80].chars
                               ^^^^^^

RuboCop version

Include the output of rubocop -V or bundle exec rubocop -V if using Bundler. Here's an example: You can see extension cop versions (e.g. rubocop-performance, rubocop-rails, and others) output by rubocop -V, include them as well. Here's an example:

rubocop -V
1.64.1 (using Parser 3.3.3.0, rubocop-ast 1.31.3, running on ruby 3.3.5) +server [arm64-darwin23]
  - rubocop-capybara 2.21.0
  - rubocop-factory_bot 2.26.1
  - rubocop-graphql 0.13.0
  - rubocop-gusto 5.3.5
  - rubocop-performance 1.21.1
  - rubocop-rails 2.25.0
  - rubocop-rake 0.6.0
  - rubocop-rspec 3.0.4
  - rubocop-sorbet 0.8.3

Background Docs: https://msp-greg.github.io/rubocop-performance/RuboCop/Cop/Performance/RedundantStringChars.html