Fix from Paul Lind that helps post-isolates V8 work with older

src/api.cc

Index: src/api.cc
===================================================================
--- src/api.cc	(revision 9686)
+++ src/api.cc	(working copy)
@@ -4005,14 +4005,15 @@
 bool v8::V8::IdleNotification() {
   // Returning true tells the caller that it need not
   // continue to call IdleNotification.
-  if (!i::Isolate::Current()->IsInitialized()) return true;
+  i::Isolate* isolate = i::Isolate::Current();
+  if (isolate == NULL || !isolate->IsInitialized()) return true;
   return i::V8::IdleNotification();
 }
 
 
 void v8::V8::LowMemoryNotification() {
   i::Isolate* isolate = i::Isolate::Current();
-  if (!isolate->IsInitialized()) return;
+  if (isolate == NULL || !isolate->IsInitialized()) return;
   isolate->heap()->CollectAllAvailableGarbage();
 }