fix ETermBase.make_function() for repeated call of de_non_penetration_p term
fix ETermBase.make_function() for repeated call of de_non_penetration_p term

- treat correctly ExpressionArg arguments

vlukes/sfepy,rc/sfepy,BubuLK/sfepy,sfepy/sfepy,BubuLK/sfepy,vlukes/sfepy,BubuLK/sfepy,rc/sfepy,vlukes/sfepy,rc/sfepy,sfepy/sfepy,sfepy/sfepy