Fix typo: use stored gallery ids, not the output list of ids

Co-authored-by: Weston Ruter <[email protected]>

Author: dmsnell

src/wp-includes/media.php

@@ -5386,9 +5386,15 @@ function get_post_galleries( $post, $html = true, $max_galleries = PHP_INT_MAX )
 
 		// Old Gallery block format as an array.
 
-		// If present, use the image IDs from the JSON blob as canonical.
+		/*
+		 * If present, use the image IDs from the JSON blob as canonical.
+		 * This is sourced above when the Block Processor first reaches
+		 * the outer `gallery` block and saved for now; this is because
+		 * once the Processor moves on to the inner text or inner blocks,
+		 * the attributes are no longer accessible.
+		 */
 		if ( ! empty( $gallery_ids ) ) {
-			foreach ( $ids as $id ) {
+			foreach ( $gallery_ids as $id ) {
 				$url = wp_get_attachment_url( $id );
 
 				if ( is_string( $url ) && ! in_array( $url, $srcs, true ) ) {