fixed bug with generate qrcode

backend/app/routers/dewar.py

@@ -103,7 +103,8 @@ async def generate_dewar_qrcode(dewar_id: int, db: Session = Depends(get_db)):
         raise HTTPException(status_code=404, detail="Dewar not found")
 
     if not dewar.unique_id:
-        raise HTTPException(status_code=400, detail="Unique ID must be set during label creation.")
+        dewar.unique_id = generate_unique_id(db)
+        db.commit()
 
     qr = qrcode.QRCode(version=1, box_size=10, border=5)
     qr.add_data(dewar.unique_id)