imrpove comment

Author: Narretz

src/ng/directive/ngOptions.js

@@ -452,7 +452,8 @@ var ngOptionsDirective = ['$compile', '$document', '$parse', function($compile,
       var removeEmptyOption = function() {
         if (!providedEmptyOption) {
           emptyOption.remove();
-        // Empty nodes with non-rendered ngIf can be comment nodes
+        // Empty options may be comment nodes if they have been removed by
+        // transclude directives such as `ngIf`
         } else if (emptyOption[0].nodeType === NODE_TYPE_ELEMENT) {
           emptyOption.removeAttr('selected');
         }