Return early for cover images that are not found

BookProvider::getCover() was already returning for no pages
returned, so this switches to API formatversion 2 and also
checks for the `missing` or `invalid` parameter in the first/only returned
page.

Bug: T370257

src/BookProvider.php

@@ -302,8 +302,13 @@ public function getCover( $cover ): ?Picture {
 			'iiprop' => 'thumbmime|dimensions|url|canonicaltitle',
 			'iiurlparam' => $urlParam,
 			'iiurlwidth' => $width,
+			'formatversion' => 2,
 		] )->wait();
-		if ( !isset( $response['query']['pages'] ) ) {
+		// Give up for invalid cover titles or those that do not exist.
+		if ( !isset( $response['query']['pages'] )
+			|| isset( $response['query']['pages'][0]['missing'] )
+			|| isset( $response['query']['pages'][0]['invalid'] )
+		) {
 			return null;
 		}