[inner-2350] need to deal with npe in performance mode

(cherry picked from commit 8fec828948)

src/main/java/com/actiontech/dble/services/mysqlauthenticate/MySQLBackAuthService.java

@@ -227,6 +227,7 @@ public class MySQLBackAuthService extends BackendService implements AuthService
         if (SystemConfig.getInstance().getUsePerformanceMode() != 1) {
             super.doHandle(null);
         } else {
+            if (task == null) return;
             if (isHandling.compareAndSet(false, true)) {
                 DbleServer.getInstance().getConcurrentBackHandlerQueue().offer(task);
             }

src/main/java/com/actiontech/dble/services/mysqlsharding/MySQLCurrentResponseService.java

@@ -23,6 +23,7 @@ public class MySQLCurrentResponseService extends MySQLResponseService {
         if (isComplexQuery()) {
             super.doHandle(null);
         } else {
+            if (task == null) return;
             if (isHandling.compareAndSet(false, true)) {
                 DbleServer.getInstance().getConcurrentBackHandlerQueue().offer(task);
             }