[new compiler] Fix incorrect accelerated lookups to id objects

When compiling JS code in the scope of a component, make sure to always
set the id object mapping, even if it is empty. Otherwise the id objects
from one scope might leak into another, leading to id object dependencies
that are invalid.

Change-Id: Ib2bca11203acd6924e8c74f9560a1ee3e00d7e39
Reviewed-by: Lars Knoll <lars.knoll@digia.com>