check if $pageInfo['no_search'] is set

The entry $pageInfo['no_search'] in function shouldIncludePageInSitemap can be empty in some cases. For example, if it is the eID start URL. Check the array and value with isset and (boolean)$pageInfo['no_search'] == 0.

Signed-off-by: Michael Reiher <reiher@wiro-consultants.de>