ExpressionUI : Fix broken menu for non-ValuePlugs.
ExpressionUI : Fix broken menu for non-ValuePlugs.

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