config: Fix for port references generated multiple times

config: Fix for port references generated multiple times

SimObjects are expected to only generate one port reference per
port belonging to them.  There is a subtle bug with using "not"
here as a VectorPort is seen as not having a reference if it is
either None or empty as per Python docs sec 9.9 for Standard operators.
Intended behavior is to only check if we have not created the reference.