Fix bug of contest statistics API

mooctest-site-server/src/main/java/cn/iselab/mooctest/site/service/impl/ContestServiceImpl.java

@@ -64,7 +64,7 @@ public class ContestServiceImpl implements ContestService {
             for (Object[] result : schoolResult) {
                 if (StringUtils.isEmpty((String) result[0])) {
                     long count = schoolMap.getOrDefault("未知", 0L);
-                    locationMap.put("未知", count + (Long) result[1]);
+                    schoolMap.put("未知", count + (Long) result[1]);
                 } else {
                     schoolMap.put((String) result[0], (Long) result[1]);
                 }