Fix get pages regular expression

[McCaulay]

A 500 error occurs when searching with the internal engine if you have brackets inside sidebar text.

Example:

- ## Example
    - [80 / 443 HTTP(S)](/{{route}}/{{version}}/example/http)

This causes the $page parameter to contain "S" in this scenario instead of "/{{route}}/{{version}}/example/http". To prevent the error, I have added a validation check on the explode array to make sure it contains more than 1 element.

To fix the issue itself, i've updated the regular expression from \(([^)]+)\) to \[.+\]\((.+)\). This expects a [something] before the brackets (url) which I believe should always exist for a valid markdown link.

[saleem-hadad]

Thank you for your help @McCaulay!