Fix integer validation when boundary value is empty string

There was an error in number validation check. If boundary value was an empty string, validation of a number always failed. This patch fixes the problem by not performing the check in these cases.

https://fedorahosted.org/freeipa/ticket/3066

install/ui/test/all_tests.html

@@ -32,6 +32,7 @@
     <script type="text/javascript" src="aci_tests.js"></script>
     <script type="text/javascript" src="widget_tests.js"></script>
     <script type="text/javascript" src="ip_tests.js"></script>
+    <script type="text/javascript" src="utils_tests.js"></script>
 </head>
 <body>
     <h1 id="qunit-header">Complete Test Suite</h1>