Issue archive page pagination is not disabled when items per page number doesn't exceed the limit

[Vitaliy-1]

Pagination doesn't work as expected because $prevUrl and $nextUrl are always not empty because of whitespaces; so, in this line: https://github.com/pkp/healthSciences/blob/master/templates/frontend/components/pagination.tpl#L20 disabled class isn't assigned in any case.
Need to trim the variable before using the not equal operator or check by ctype_space, or regex.