Only consider article ID if A/B test enabled

The article ID shouldn't matter for display of table of contents
unless the A/B test is enabled.

This also has the added benefit of making the content provider
work with table of contents on articles again (content provider articles
always have a page id of 0)

Change-Id: I6af5e1476827828d0974ecbb110476ac1e5dc0c9

includes/SkinVector22.php

@@ -64,14 +64,13 @@ class SkinVector22 extends SkinVector {
 
 		if (
 			!$title ||
-			$title->getArticleID() === 0 ||
 			$title->isMainPage()
 		) {
 			return false;
 		}
 
 		if ( $this->isTOCABTestEnabled() ) {
-			return true;
+			return $title->getArticleID() !== 0;
 		}
 
 		return $this->isTOCEnabled();