webui: set default extras as empty array to prevent compact() errors

PHP compact() function will create php error when $args is an
empty array.

See: zendframework/zend-view#170

Fixes #1205: HeadLink.php error with PHP 7.3

webui/vendor/zendframework/zend-view/src/Helper/HeadLink.php

@@ -395,6 +395,8 @@ public function createDataStylesheet(array $args)
             }
         }
 
+        $extras = [];
+
         if (0 < count($args) && is_array($args[0])) {
             $extras = array_shift($args);
             $extras = (array) $extras;
@@ -443,6 +445,8 @@ public function createDataAlternate(array $args)
         $type  = array_shift($args);
         $title = array_shift($args);
 
+        $extras = [];
+
         if (0 < count($args) && is_array($args[0])) {
             $extras = array_shift($args);
             $extras = (array) $extras;