After [31645], for the `default` `case`, return the result of checking the extension against the passed type.

See #25275.


git-svn-id: https://develop.svn.wordpress.org/trunk@31646 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/post.php

@@ -5106,9 +5106,10 @@ function wp_attachment_is( $type, $post_id = 0 ) {
 
 	case 'video':
 		return in_array( $ext, wp_get_video_extensions() );
-	}
 
-	return false;
+	default:
+		return $type === $ext;
+	}
 }
 
 /**