Make the VM resilient to a confusion between a NULL instructions snapshot and instructions snapshot…

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 abfb3458bfe5b94b3ebb492d30fde544158edd15..40e8987152ffd60ba89b584c7bb03b295b6e89ae 100644
--- a/runtime/vm/clustered_snapshot.cc
+++ b/runtime/vm/clustered_snapshot.cc
@@ -5479,10 +5479,10 @@ RawApiError* FullSnapshotReader::ReadVMSnapshot() {
     return error;
   }
 
-  if (instructions_buffer_ != NULL) {
+  if (Snapshot::IncludesCode(kind_)) {
+    ASSERT(instructions_buffer_ != NULL);
     thread_->isolate()->SetupInstructionsSnapshotPage(instructions_buffer_);
-  }
-  if (data_buffer_ != NULL) {
+    ASSERT(data_buffer_ != NULL);
     thread_->isolate()->SetupDataSnapshotPage(data_buffer_);
   }
 
@@ -5501,10 +5501,10 @@ RawApiError* FullSnapshotReader::ReadIsolateSnapshot() {
     return error;
   }
 
-  if (instructions_buffer_ != NULL) {
+  if (Snapshot::IncludesCode(kind_)) {
+    ASSERT(instructions_buffer_ != NULL);
     thread_->isolate()->SetupInstructionsSnapshotPage(instructions_buffer_);
-  }
-  if (data_buffer_ != NULL) {
+    ASSERT(data_buffer_ != NULL);
     thread_->isolate()->SetupDataSnapshotPage(data_buffer_);
   }