Support caller-allocated GValue in vfunc marshalling
In the gobject-introspection test suite we have the following test of a GValue being returned from a vfunc:
/**
* gi_marshalling_tests_object_vfunc_caller_allocated_out_parameter:
* @a: (out):
*/
void gi_marshalling_tests_object_vfunc_caller_allocated_out_parameter(GIMarshallingTestsObject* self, GValue* a);
Executing that test as it's intended to be executed (by creating an object that implements the vfunc and returns a value to be packed into the GValue) will throw the following exception:
Don't know how to convert GType (null) to JavaScript object
Verify the fix by un-disabling the test in testGIMarshalling.js and checking that it passes correctly.