Issue with page()->url('+')

[Zeka]

Hi. 

I have an issue with $page->url('+') and $page->url('-') where produce wrong URLs like site.com/some-page/-/page1/ and not site.com/some-page/page1/ etc.

I have tested it on the latest dev version. 

I tracked down it to this line https://github.com/processwire/processwire/blob/d8945198f4a6a60dab23bd0462e8a6285369dcb9/wire/core/PageTraversal.php#L616

I think that there should be addition check like

'urlSegmentStr' => is_string($options) && !in_array($options, array('+', '-')) ? $options : '',

Before opening an issue I would like to ask to confirm it.

Thansk.