Fix void_function_in_ternary incorrectly triggered with if statement

[yuya-okuse]

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Fixes #5611

This PR corrects that VoidFunctionInTernaryConditionRule incorrectly triggered with if statement. This new rule is triggered or not depending on the return type of the function.

[SwiftLintBot]

	2 Warnings
:warning:	If this is a user-facing change, please include a CHANGELOG entry to credit yourself! You can find it at CHANGELOG.md.
:warning:	This PR may need tests.

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* Fix void_function_in_ternary incorrectly triggered with if statement.  
  [u-abyss](https://github.com/u-abyss)
  [#issue_number](https://github.com/realm/SwiftLint/issues/issue_number)

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[yuya-okuse]

@SimplyDanny Added handling of nested if and switch statements. I have a question. I believe that when you initialize a variable in an if or switch expression, the compiler prevents you from writing a statement that returns void in it. If there is an appropriate case for initializing a variable in an if or switch expression, I would appreciate it if you could let me know.

[SimplyDanny]

@SimplyDanny Added handling of nested if and switch statements. I have a question. I believe that when you initialize a variable in an if or switch expression, the compiler prevents you from writing a statement that returns void in it. If there is an appropriate case for initializing a variable in an if or switch expression, I would appreciate it if you could let me know.

Can you provide an example?

The code

func f(i: Int) -> Int {
  if i > 1 {
    let j = i - 1
    j
  } else {
    0
  }
}

wouldn't compile. There you need the return before j.