Allow comment body "No" in comment validation

Summary

User Lensflare reports that a comment with body No is rejected, possibly interpreted as number. Comment by D-04got10-01 confirms the bug.

Steps to Reproduce

1. Submit a comment with body No.

Expected Behaviour

Comment validation allows No as a comment body.

Actual Behaviour

Comment with body No is rejected.

Environment

Not provided.

Reported by retoor via DevPlace.