fix(用例管理): 修复用例管理关联场景显示失败问题

--bug=1039889 --user=郭雨琦 https://www.tapd.cn/55049933/bugtrace/bugs/view/1155049933001039889

backend/services/case-management/src/main/java/io/metersphere/functional/mapper/ExtFunctionalCaseTestMapper.xml

@@ -32,8 +32,8 @@
         fct.create_time,
         p.name as projectName,
         v.name as versionName,
-        NULLIF(atc.name, scenario.name) as sourceName,
-        NULLIF(atc.num, scenario.num) as sourceNum
+        IF(atc.name is not null, atc.name, scenario.name) as sourceName,
+        IF(atc.num is not null, atc.num, scenario.num) as sourceNum
         FROM
         functional_case_test fct
         LEFT JOIN project p ON fct.project_id = p.id