refactor if structure

[lm-noshiro]

What this patch does to fix the issue.

• Refactored if statement structures.
  • Replaced unnecessary use of elif with if if it's immediately after return / raise statement.
  • Changed to use early return pattern

Link to any relevant issues or pull requests.

#1058

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[iizukak]

@lm-noshiro Thank you for fixing some points. Can you check conflicted files?