Reduce the time voucher rows are locked when creating orders

thallium-backend/src/routes/orders.py

@@ -21,15 +21,16 @@ async def create_order(request: Request, db: DBSession, client: PrintfulClient,
     If the voucher does not have enough funds, the order is cancelled.
     """
     voucher: Voucher = request.state.voucher
-    stmt = select(DBVoucher).where(DBVoucher.id == voucher.id).with_for_update()
-    db_voucher = await db.scalar(stmt)
 
     resp = await client.post(
         "/orders/estimate-costs",
         json=order.as_printful_payload(voucher),
         params={"confirm": False},
     )
     resp.raise_for_status()
+
+    stmt = select(DBVoucher).where(DBVoucher.id == voucher.id).with_for_update()
+    db_voucher = await db.scalar(stmt)
     cost = OrderCosts.model_validate(resp.json()["result"]["costs"])
     if cost.total > db_voucher.balance:
         raise HTTPException(