fix(dropdown): forceSelection trigger event with null addition

When allowAdditions is handled by click event, forceSelection triggers event click again, but with allowAdditions removed can't find the item.
As far as I know I can't know if the event calling this method is the original click or forceSelection trigger, so what I did is: if there's no element and allowAdditions and forceSelection is set to true return null.

Author: TheJltres

src/definitions/modules/dropdown.js

@@ -1945,8 +1945,8 @@ $.fn.dropdown = function(parameters) {
               return ($choice.data(metadata.text) !== undefined)
                 ? $choice.data(metadata.text)
                 : (preserveHTML)
-                  ? $choice.html().trim()
-                  : $choice.text().trim()
+                  ? $choice.html() && $choice.html().trim()
+                  : $choice.text() && $choice.text().trim()
               ;
             }
           },