fix

examcloud-core-oe-admin-api-provider/src/main/java/cn/com/qmth/examcloud/core/oe/admin/api/controller/OfflineExamController.java

@@ -202,7 +202,7 @@ public class OfflineExamController extends ControllerSupport {
                 String fileName = file.getOriginalFilename();
                 sb.append(fileName).append(",");
         	}
-        	sb.deleteCharAt(sb.length());
+        	sb.deleteCharAt(sb.length()-1);
         	log.error("batchSubmitPaper-duplicate:"+examRecordDataId+":"+sb);
         	throw new StatusException("000500", "上传"+upperFileType+"类型文件时只能传一个文件");
         }