fix:修改教师名称字段是否返回的判断方法（?. => &&）

src/modules/course-manage/components/LiveCourseList.jsx

@@ -177,7 +177,7 @@ class LiveCourseList extends React.Component {
                     </span>
                     </span>
                   </div>
                   </div>
                   <div className='teacher-assistant'>
                   <div className='teacher-assistant'>
-                    {record.teacherName?.length > 4 ? (
+                    {record.teacherName && record.teacherName.length > 4 ? (
                       <Tooltip title={record.teacherName}>
                       <Tooltip title={record.teacherName}>
                         <span className='teacher'>讲师：{record.teacherName}</span>
                         <span className='teacher'>讲师：{record.teacherName}</span>
                       </Tooltip>
                       </Tooltip>