fixed has_alt_urls? and has_redirect_to_url? conditions.

`!alt_urls(page_or_post).empty? && !alt_urls(page_or_post).nil?` were redundant conditions whenever value of `page_or_post.data['redirect_from'] == nil`. In this case `alt_urls = [nil]`
`!alt_urls(page_or_post).nil?`  was redundant because final output of `alt_urls` is always an array

Also, I think `redirect_to_url` should return a single url and not an array, in this way the name would make more sense. If you agree than I could make the necessary changes in the code and resubmit the pull request.