Fix off-by-one issue in clustered snapshot implementation and api impl

runtime/vm/clustered_snapshot.cc

Index: runtime/vm/clustered_snapshot.cc
diff --git a/runtime/vm/clustered_snapshot.cc b/runtime/vm/clustered_snapshot.cc
index 7fce179d5d8377dc5f19fd7cd106730a76161feb..db4c9c0aff94ec58fda5d8844c41485e74403bec 100644
--- a/runtime/vm/clustered_snapshot.cc
+++ b/runtime/vm/clustered_snapshot.cc
@@ -4312,7 +4312,7 @@ SerializationCluster* Serializer::NewClusterForClass(intptr_t cid) {
   return NULL;
 #else
   Zone* Z = zone_;
-  if ((cid > kNumPredefinedCids) ||
+  if ((cid >= kNumPredefinedCids) ||
       (cid == kInstanceCid) ||
       RawObject::IsTypedDataViewClassId(cid)) {
     Push(isolate()->class_table()->At(cid));
@@ -4636,7 +4636,7 @@ DeserializationCluster* Deserializer::ReadCluster() {
   intptr_t cid = ReadCid();
 
   Zone* Z = zone_;
-  if ((cid > kNumPredefinedCids) ||
+  if ((cid >= kNumPredefinedCids) ||
       (cid == kInstanceCid) ||
       RawObject::IsTypedDataViewClassId(cid)) {
     return new (Z) InstanceDeserializationCluster(cid);