fix(stream): fix error in generating checkpoint.

source/libs/stream/src/streamExec.c

@@ -423,17 +423,18 @@ int32_t streamExecForAll(SStreamTask* pTask) {
     }
 
     if (pTask->info.taskLevel == TASK_LEVEL__SINK) {
+      ASSERT(pInput->type == STREAM_INPUT__DATA_BLOCK || pInput->type == STREAM_INPUT__CHECKPOINT);
+
       if (pInput->type == STREAM_INPUT__DATA_BLOCK) {
         qDebug("s-task:%s sink task start to sink %d blocks", id, batchSize);
         streamTaskOutputResultBlock(pTask, (SStreamDataBlock*)pInput);
         continue;
-      }
-    } else {
-      ASSERT(pInput->type == STREAM_INPUT__CHECKPOINT);
+      } else {  // for sink task, do nothing.
         ASSERT(pTask->status.taskStatus == TASK_STATUS__CK);
         pTask->status.taskStatus = TASK_STATUS__CK_READY;
         return 0;
       }
+    }
 
     int64_t st = taosGetTimestampMs();
     qDebug("s-task:%s start to process batch of blocks, num:%d", id, batchSize);