fixed __toString() methods that can return false under certain circumstancies

src/Symfony/Components/DependencyInjection/Resource/FileResource.php

@@ -39,7 +39,7 @@ class FileResource implements ResourceInterface
      */
     public function __toString()
     {
-        return $this->resource;
+        return (string) $this->resource;
     }
 
     /**

src/Symfony/Components/Routing/Resource/FileResource.php

@@ -39,7 +39,7 @@ class FileResource implements ResourceInterface
      */
     public function __toString()
     {
-        return $this->resource;
+        return (string) $this->resource;
     }
 
     /**