add test: variable with units but no name
add test: variable with units but no name

nickerso/libcellml,hsorby/libcellml,cellml/libcellml,MichaelClerx/libcellml,cellml/libcellml,hsorby/libcellml,MichaelClerx/libcellml,libcellml/buildbot-testing,cellml/libcellml,nickerso/libcellml,cellml/libcellml,libcellml/buildbot-testing,MichaelClerx/libcellml,nickerso/libcellml,hsorby/libcellml,hsorby/libcellml,nickerso/libcellml