OO-3898: override coach collect date if user submit its work

src/main/java/org/olat/course/nodes/gta/manager/GTAManagerImpl.java

@@ -1487,6 +1487,8 @@ public class GTAManagerImpl implements GTAManager {
 		TaskImpl taskImpl = (TaskImpl)task;
 		taskImpl.setSubmissionDate(new Date());
 		taskImpl.setSubmissionNumOfDocs(numOfDocs);
+		taskImpl.setCollectionDate(null);
+		taskImpl.setCollectionNumOfDocs(null);
 		return updateTask(task, review, cNode, by);
 	}