lazy instantiation of the default isolate

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index 6d627499826e75f99b8494ed82e0f6bf01eabb3e..c307d8df4c4816fa0ac879a4926d1fb22af868b2 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -5030,14 +5030,13 @@ void v8::V8::SetArrayBufferAllocator(
 
 
 bool v8::V8::Dispose() {
-  i::Isolate* isolate = i::Isolate::Current();
-  if (!ApiCheck(isolate != NULL && isolate->IsDefaultIsolate(),
+  i::Isolate* isolate = i::Isolate::UncheckedCurrent();
+  if (!ApiCheck(isolate == NULL || isolate->IsDefaultIsolate(),
                 "v8::V8::Dispose()",
                 "Use v8::Isolate::Dispose() for a non-default isolate.")) {
     return false;
   }
-  i::V8::TearDown();
-  return true;
+  return i::V8::TearDown();
 }