internal: small fix to e2e test

Change-Id: I5f817a01eaae5fbf96f3a680c5c6383dbd98061e
Reviewed-on: https://code-review.googlesource.com/c/36530
Reviewed-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Eno Compton <enocom@google.com>
diff --git a/pubsub/internal/longtest/endtoend_test.go b/pubsub/internal/longtest/endtoend_test.go
index dd1d362..8dfa55f 100644
--- a/pubsub/internal/longtest/endtoend_test.go
+++ b/pubsub/internal/longtest/endtoend_test.go
@@ -267,7 +267,7 @@
 		prev := c.totalRecvd
 		err := sub.Receive(ctx2, c.process)
 		t.Logf("%s: end receive; read %d", id, c.totalRecvd-prev)
-		if serr, _ := status.FromError(err); serr.Code() != codes.Canceled {
+		if serr, _ := status.FromError(err); err != nil && serr.Code() != codes.Canceled {
 			panic(err)
 		}
 		select {