Skip empty page template meta

[willmot]

The check for false !== $custom_page_template is too strict as get_post_meta returns an empty string rather than (bool) false. This incorrectly caused the $custom_page_template if statement to return true which then caused a locate_template( array( '' ) ); further down which would fail thus causing pages to fall back to using single.php instead of page.php.

This PR loosens the $custom_page_template check so that any falsey value will cause a fallback to page.php.

The actual code change is in c8f09ce in-case you want just that and not the associated whitespace cleanup in 6f908e1

Would be great to get this merged as it's affecting a current project.

[johnbillion]

Merge into develop in 500cc7c

[willmot]

:+1: