get_page_link() doesn't check if a valid post object is returned before trying to access its properties

[rodrigosprimo]

If get_page_link() receives an invalid post ID as the first parameter it will generate a PHP notice:

$ wp shell
>>> get_page_link( -1 )
PHP Notice:  Trying to get property of non-object in /vagrant/www/wccore/htdocs/wp-includes/link-template.php on line 317

Should a check be added to prevent this notice from happening? I'm happy to submit a patch. I'm just not sure what is the best way to handle this. Should the function return null if get_post() can't find a valid post? Should it call _doing_it_wrong()? Something else?

…properties

Modified get_page_link() function to check if post object is found before proceeding to access its properties.

Trac ticket: 44497