Front page displays: Fix same static page warning

[zeo]

Front page display-> static page; if you choose same page for both Front page and Posts page a warning message will appear.

But if you choose static page without selecting a page for Front page, Posts Page and use the default "--Select--" for both, no warning message displayed. This will cause error, since the value for page_on_front will 0 but page_for_posts is set with no value. Warning message should be displayed.

Adding option_none_value=0 to wp_dropdown_pages will solve the issue.

[zeo]

Fix warning for same page static page

[zeo]

Perhaps should include these in wp-admin/includes/schema.php too:

// 3.0
'page_for_posts' => 0,
'page_on_front' => 0,

[nacin]

Attached diff takes zeo's patch a bit further.

The reason why no warning showed up in the admin was because only one was getting sanitized as an integer. Since we're now going to use show_option_none => 0, sanitizing it won't help any, but since I caught it, we might as well also sanitize it (a review we need to do in a future release more thoroughly).

I also added a little code to catch bad values and fix them when showing options-reading (thus after saving). It does it silently, but I think that is perfectly acceptable for now.

[nacin]

Of note, the code to fix the bad show_on_front value (bad when both of the options are 0) is required to fix the notice.

[wpmuguru]

(In [15224]) fix warning when page on front missing, see #13830

[nacin]

[15224] only band-aids the real problem; a lot of WP_Query will likely be confused on that page view.

[nacin]

(In [15227]) Fix warnings related to static pages. props zeo for initial patch. fixes #13830.