fix: 不选择用户后清除优惠券，修改优惠券可用数量计算公式为数量-退菜-退款

src/views/tool/Instead/components/order.vue

@@ -346,6 +346,7 @@ const seatAmount = computed(() => {
 watch(
   () => props.user.id,
   (newval) => {
+    quansSelArr.value = [];
     if (newval !== "") {
       pointsInit();
     }