Fix VoteSite caching

Codacy identified an unused local variable `$allSites` in the function
`VoteSite::getAllSites`. This was supposed to be `$ALL_SITES`, and so
the intended caching was not working.

The effect of not caching here is very minimal, since there are no
database queries involved.

lib/Default/VoteSite.class.php

@@ -43,7 +43,7 @@ private static function getAllSiteData() {
 
 	public static function getAllSites() {
 		static $ALL_SITES;
-		if (!isset($allSites)) {
+		if (!isset($ALL_SITES)) {
 			$ALL_SITES = array(); // ensure this is set
 			foreach (self::getAllSiteData() as $linkID => $siteData) {
 				$ALL_SITES[$linkID] = new VoteSite($linkID, $siteData);