fix(用例评审): 修复用例评审获取评论时会出现的空指针问题

backend/src/main/java/io/metersphere/track/service/TestCaseCommentService.java

@@ -61,7 +61,8 @@ public class TestCaseCommentService {
         testCaseComments.forEach(testCaseComment -> {
             String authorId = testCaseComment.getAuthor();
             User user = userMapper.selectByPrimaryKey(authorId);
-            testCaseComment.setAuthor(user.getName());
+            String author = user == null ? authorId : user.getName();
+            testCaseComment.setAuthor(author);
         });
         return testCaseComments;
     }