AuxiliaryConnectionsGadget : Fix connections to empty gadgets
AuxiliaryConnectionsGadget : Fix connections to empty gadgets

These can occur when a nested plug has an input but no nodule, and the parent plug has a nodule and no children with nodules. Connections into the colour components of the OpenGL Constant shader meet these criteria.

hradec/gaffer,lucienfostier/gaffer,andrewkaufman/gaffer,lucienfostier/gaffer,johnhaddon/gaffer,boberfly/gaffer,appleseedhq/gaffer,appleseedhq/gaffer,GafferHQ/gaffer,johnhaddon/gaffer,boberfly/gaffer,GafferHQ/gaffer,GafferHQ/gaffer,appleseedhq/gaffer,andrewkaufman/gaffer,johnhaddon/gaffer,ImageEngine/gaffer,johnhaddon/gaffer,hradec/gaffer,andrewkaufman/gaffer,johnhaddon/gaffer,boberfly/gaffer,GafferHQ/gaffer,andrewkaufman/gaffer,ImageEngine/gaffer,hradec/gaffer,lucienfostier/gaffer,boberfly/gaffer,andrewkaufman/gaffer,GafferHQ/gaffer,appleseedhq/gaffer,hradec/gaffer,ImageEngine/gaffer,ImageEngine/gaffer,lucienfostier/gaffer,hradec/gaffer