[Bug]: 多轴图数据缺失的时候，tooltip title 显示异常 #6699

Describe the bug / 问题描述

tooltip显示相关问题，柱状图堆叠+折线图，部分时间X轴对应的Y轴没有值，这种情况显示的tooltip异常

import { Chart } from '@antv/g2';

const chart = new Chart({
  container: 'container',
  autoFit: true,
});

const data = [
  { time: '10:10', call: 4, waiting: 2, people: 2 },
  { time: '10:15', call: 2, waiting: 6, people: 3 },
  { time: '10:20', call: 13, waiting: 2, people: 5 },
  { time: '10:25', call: 9, waiting: 9, people: 1 },
  { time: '10:30', call: 5, waiting: 6, people: 3 },
  { time: '10:35', call: 8, waiting: null, people: null },
  { time: '10:40', call: 13, waiting: 3, people: 2 },
];

chart.data(data);

chart
  .interval()
  .encode('x', 'time')
  .encode('y', 'waiting')
  .encode('color', () => 'waiting')

chart
  .interval()
  .encode('x', 'time')
  .encode('y', 'people')
  .encode('color', () => 'people')

chart
  .line()
  .encode('x', 'time')
  .encode('y', 'call')
  .encode('color', () => 'call')

chart.render();

Reproduction link / 复现链接

No response

Steps to Reproduce the Bug or Issue / 重现步骤

No response

Version / 版本

🆕 5.x

OS / 操作系统

• macOS
• Windows
• Linux
• Others / 其他

Browser / 浏览器

• Chrome
• Edge
• Firefox
• Safari (Limited support / 有限支持)
• IE (Nonsupport / 不支持)
• Others / 其他