bug #2043 Fix load cache (MaCroTux)

This PR was squashed before being merged into the 1.x branch (closes #2043).

Discussion
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Fix load cache

In PHP7 @ do not works and it is resource expensive, switching to if statement.

Commits
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b5df3d1 Fix load cache

lib/Twig/Cache/Filesystem.php

@@ -46,7 +46,7 @@ public function generateKey($name, $className)
      */
     public function load($key)
     {
-        @include_once $key;
+        if (file_exists($key)) @include_once $key;
     }
 
     /**