Fixes #17103 Fix the empty combobox

This fix is for the problem with the the initial combobox label being empty, it is fixed in dijit/form/_FormSelectWidget.js.  There is another part of the fix in dojox/form/CheckedMultiSelect.js which has to do with the menu not displaying the checkboxes, and it also has updated the mvc test which tests the problem which introduced this problem (the empty combobox), to be sure this fix for this does not regress that.