fix getColumnTitle bug
fix getColumnTitle bug

title: <div>
           <span>title</span>
           null
        </div>
elevensky/ant-design,icaife/ant-design,icaife/ant-design,icaife/ant-design,zheeeng/ant-design,ant-design/ant-design,ant-design/ant-design,ant-design/ant-design,zheeeng/ant-design,icaife/ant-design,elevensky/ant-design,zheeeng/ant-design,elevensky/ant-design,elevensky/ant-design,ant-design/ant-design,zheeeng/ant-design