Fix for bug 3324285 jsc::bindings::convertValueToNPVariant fails to findroot() and...

Fix for bug 3324285 jsc::bindings::convertValueToNPVariant fails to findroot() and passes objects as npvariant_void

Also trying lexicalGlobalObject as root object, the comment for
lexicalGlobalObject says:
// Global object in which the currently executing code was defined.
// Differs from dynamicGlobalObject() during function calls across web browser frames.

I'm guessing that is the case here.

Webkit bug:
https://bugs.webkit.org/show_bug.cgi?id=55216

Change-Id: I61b3df93261e3688f022cde058845b1e3dfedb38