[FrameworkBundle] Enable assets with templates only if the Asset component is installed

Author: hason

DependencyInjection/Configuration.php

@@ -52,7 +52,7 @@ public function getConfigTreeBuilder()
 
         $rootNode
             ->beforeNormalization()
-                ->ifTrue(function ($v) { return !isset($v['assets']) && isset($v['templating']); })
+                ->ifTrue(function ($v) { return !isset($v['assets']) && isset($v['templating']) && class_exists(Package::class); })
                 ->then(function ($v) {
                     $v['assets'] = array();