tweak formatSelection for select2#400

Author: ivaynberg

select2.js

@@ -2059,8 +2059,10 @@
                 val = this.getVal(),
                 formatted;
 
-            formatted=this.opts.formatSelection(data, choice);
-            choice.find("div").replaceWith("<div>"+this.opts.escapeMarkup(formatted)+"</div>");
+            formatted=this.opts.formatSelection(data, choice.find("div"));
+            if (formatted != undefined) {
+                choice.find("div").replaceWith("<div>"+this.opts.escapeMarkup(formatted)+"</div>");
+            }
             choice.find(".select2-search-choice-close")
                 .bind("mousedown", killEvent)
                 .bind("click dblclick", this.bind(function (e) {