do not break when loading schemas from network paths on Windows

src/Symfony/Component/DependencyInjection/Loader/XmlFileLoader.php

@@ -614,6 +614,8 @@ class XmlFileLoader extends FileLoader
                     array_shift($parts);
                     $locationstart = 'phar:///';
                 }
+            } elseif ('\\' === \DIRECTORY_SEPARATOR && 0 === strpos($location, '\\\\')) {
+                $locationstart = '';
             }
             $drive = '\\' === \DIRECTORY_SEPARATOR ? array_shift($parts).'/' : '';
             $location = $locationstart.$drive.implode('/', array_map('rawurlencode', $parts));