僱用人安全保護義務 民法第483條之1 過勞自殺 債務不履行 僱用人安全保護義務之類推適用 類似僱傭契約之法律關係 Employer's consideration duty for safe Civil Code article 483-1 Over-work suicides Default on an obligation Analogy application for employer's consideration duty for safe Relationship of quasi employment contract