fix options with empty values. fixes select2#1497

Author: ivaynberg

select2.js

@@ -1,4 +1,4 @@
-/*
+/*
 Copyright 2012 Igor Vaynberg
 
 Version: @@ver@@ Timestamp: @@timestamp@@
@@ -2057,7 +2057,8 @@ the specific language governing permissions and limitations under the Apache Lic
 
         isPlaceholderOptionSelected: function() {
             var placeholderOption;
-            return ((placeholderOption = this.getPlaceholderOption()) !== undefined && placeholderOption.is(':selected')) ||
+            return this.opts.placeholder &&
+                ((placeholderOption = this.getPlaceholderOption()) !== undefined && placeholderOption.is(':selected')) ||
                    (this.opts.element.val() === "") ||
                    (this.opts.element.val() === undefined) ||
                    (this.opts.element.val() === null);