fix

stmms-web/src/main/java/cn/com/qmth/stmms/admin/exam/StudentController.java

@@ -314,7 +314,7 @@ public class StudentController extends BaseExamController {
                 if (previous != null && previous.getId() != null) {
                     student = updatePrevious(student, previous);
                     updateList.add(student);
-                } else {
+                } else if(previous == null){
                     saveList.add(student);
                 }
                 saveMap.put(student.getExamNumber(), student);