Return correct value from validateVariableInterface in Validator.
Return correct value from validateVariableInterface in Validator.

nickerso/libcellml,cellml/libcellml,hsorby/libcellml,hsorby/libcellml,cellml/libcellml,MichaelClerx/libcellml,nickerso/libcellml,MichaelClerx/libcellml,cellml/libcellml,nickerso/libcellml,hsorby/libcellml,MichaelClerx/libcellml,hsorby/libcellml,cellml/libcellml,nickerso/libcellml