External snapshot: allow empty snapshot for external snapshot.

src/snapshot/snapshot.h

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/isolate.h"
 #include "src/snapshot/serialize.h"
 
 #ifndef V8_SNAPSHOT_SNAPSHOT_H_
 #define V8_SNAPSHOT_SNAPSHOT_H_
 
@@ skipping 20 matching lines @@
   // Initialize the Isolate from the internal snapshot. Returns false if no
   // snapshot could be found.
   static bool Initialize(Isolate* isolate);
   // Create a new context using the internal partial snapshot.
   static MaybeHandle<Context> NewContextFromSnapshot(
       Isolate* isolate, Handle<JSGlobalProxy> global_proxy,
       Handle<FixedArray>* outdated_contexts_out);
 
   static bool HaveASnapshotToStartFrom(Isolate* isolate) {
     // Do not use snapshots if the isolate is used to create snapshots.
-    return isolate->snapshot_blob() != NULL;
+    return isolate->snapshot_blob() != NULL &&
+           isolate->snapshot_blob()->data != NULL;
   }
 
   static bool EmbedsScript(Isolate* isolate);
 
   static uint32_t SizeOfFirstPage(Isolate* isolate, AllocationSpace space);
 
 
   // To be implemented by the snapshot source.
   static const v8::StartupData* DefaultSnapshotBlob();
 
@@ skipping 32 matching lines @@
   DISALLOW_IMPLICIT_CONSTRUCTORS(Snapshot);
 };
 
 #ifdef V8_USE_EXTERNAL_STARTUP_DATA
 void SetSnapshotFromFile(StartupData* snapshot_blob);
 #endif
 
 } }  // namespace v8::internal
 
 #endif  // V8_SNAPSHOT_SNAPSHOT_H_