fix: extract_worker OFFICE_FORMATS 블록에 return 누락 수정

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/workers/extract_worker.py

@@ -117,6 +117,7 @@ async def process(document_id: int, session: AsyncSession) -> None:
             raise RuntimeError(f"LibreOffice 텍스트 추출 timeout (60s)")
         finally:
             tmp_input.unlink(missing_ok=True)
+        return
 
     # 미지원 포맷
     doc.extracted_text = ""