pubsub: change MaxExtensionPeriod default

Change-Id: Iec4cae40d09170cbb3716038c6f76d66e1a9fb27
Reviewed-on: https://code-review.googlesource.com/c/gocloud/+/52570
Reviewed-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Alex Hong <hongalex@google.com>
diff --git a/pubsub/subscription.go b/pubsub/subscription.go
index 3d8229d..2d36577 100644
--- a/pubsub/subscription.go
+++ b/pubsub/subscription.go
@@ -419,7 +419,7 @@
 // DefaultReceiveSettings holds the default values for ReceiveSettings.
 var DefaultReceiveSettings = ReceiveSettings{
 	MaxExtension:           60 * time.Minute,
-	MaxExtensionPeriod:     -1,
+	MaxExtensionPeriod:     0,
 	MaxOutstandingMessages: 1000,
 	MaxOutstandingBytes:    1e9, // 1G
 	NumGoroutines:          1,