don't raise warnings when exception is thrown
don't raise warnings when exception is thrown

`array_map()` raises a warning when an exception is thrown inside the
callback (see https://bugs.php.net/bug.php?id=55416). To avoid these
warnings, `selectorToXPath()` is applied inside the loop.

oswaldderiemaecker/CssSelector,symfony/CssSelector,symfony/css-selector,symfony/css-selector,oswaldderiemaecker/CssSelector,symfony/CssSelector