Fixed possible 'Undefined offset' warning.

unset() does not renumber the array keys. An 'Undefined offset' warning may be issued when mixing named and unnamed parameters with CakeEmail handler.

Test case:

CakeLog::config('default', array(
	'engine' => 'Monolog.MonologLogger',
	'search' => APP.'Vendor/',
	'channel' => 'app',
	'handlers' => array(
		// ...
		'CakeEmail' => array(
			'me@somewhere.com',
			'Email Subject',
			'default',
			400 /* minimum level >= Logger::ERROR */,
			'formatters' => array(
				'Line' => array("...%message%")
			),
			'processors' => array(
				'Introspection',
			),
			'search' => CakePlugin::path('Monolog').DS.'Lib'.DS.'Log'.DS.'Handler',
		),
	)
));

Warning message:

Notice (8): Undefined offset: 4 [APP/Plugin/Monolog/Lib/Log/Engine/MonologLogger.php, line 127]