WeldInstance.Handle#get() behaves unexpectedly

If you invoke WeldInstance.Handler#get() for a Handler whose contextual reference was already destroyed, we currently return the same instance.
This is unexpected and it would make a lot more sense to instead throw an exception.

For Weld 5, this has been fixed as part of WELD-2685, but we still need to fix this for Weld 3 and 4.