fix(uiSelectCtrl): ensureHighlightVisible triggered with closed dropdown
fix(uiSelectCtrl): ensureHighlightVisible triggered with closed dropdown

This fix ensures that the dropdown actually is open before calling
_ensureHighlightVisible.

Fixes: #2050

Jefiozie/ui-select,Jefiozie/ui-select,Jefiozie/ui-select,angular-ui/ui-select,angular-ui/ui-select,angular-ui/ui-select