Fix potential crash if a context with no bindings is released (issue #736).

git-svn-id: https://chromiumembedded.googlecode.com/svn/trunk@899 5089003a-bbd8-11dd-ad1f-f1f9622dbc98

libcef/renderer/v8_impl.cc

@@ -119,6 +119,9 @@ class CefV8TrackManager {
 
       v8::Handle<v8::Object> object = context->Global();
       v8::Handle<v8::Value> value = object->GetHiddenValue(context_state_key_);
+      if (value.IsEmpty())
+        return;
+
       scoped_refptr<CefV8ContextState> state =
           static_cast<CefV8ContextState*>(v8::External::Unwrap(value));
       state->Detach();