fix(测试跟踪): 集成Zentao同步缺陷附件报错问题

--bug=1023370 --user=宋昌昌 【测试跟踪】缺陷管理-集成Zentao-同步缺陷-后端报错 https://www.tapd.cn/55049933/s/1338597

test-track/backend/src/main/java/io/metersphere/service/IssuesService.java

@@ -1018,6 +1018,9 @@ public class IssuesService {
                         .collect(Collectors.toSet());
 
                 List<PlatformAttachment> syncAttachments = attachmentMap.get(issueId);
+                if (CollectionUtils.isEmpty(syncAttachments)) {
+                    continue;
+                }
                 for (PlatformAttachment syncAttachment : syncAttachments) {
                     String fileName = syncAttachment.getFileName();
                     String fileKey = syncAttachment.getFileKey();