make consumeMessageBatchMaxSize default value consistent with java client (#660)

Co-authored-by: zhangxu16 <zhangxu16@xiaomi.com>
diff --git a/consumer/push_consumer.go b/consumer/push_consumer.go
index efd373f..ec44a1e 100644
--- a/consumer/push_consumer.go
+++ b/consumer/push_consumer.go
@@ -501,7 +501,7 @@
 
 	if pc.option.ConsumeMessageBatchMaxSize < 1 || pc.option.ConsumeMessageBatchMaxSize > 1024 {
 		if pc.option.ConsumeMessageBatchMaxSize == 0 {
-			pc.option.ConsumeMessageBatchMaxSize = 512
+			pc.option.ConsumeMessageBatchMaxSize = 1
 		} else {
 			rlog.Error("option.ConsumeMessageBatchMaxSize out of range [1, 1024]", nil)
 		}