AnalyserModel: make sure that hasExternalVariables() is tested.
AnalyserModel: make sure that hasExternalVariables() is tested.

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