[INTERNAL] sap.m.ComboBox: add unit test to improve code coverage
[INTERNAL] sap.m.ComboBox: add unit test to improve code coverage

Change-Id: Ied90e94ba50ab11727746a4033e8c4d9ff1413d6

SAP/openui5,nzamani/openui5,SQCLabs/openui5,SAP/openui5,cschuff/openui5,olirogers/openui5,SAP/openui5,SAP/openui5,nzamani/openui5,olirogers/openui5,olirogers/openui5,cschuff/openui5,cschuff/openui5,SQCLabs/openui5,SQCLabs/openui5,nzamani/openui5