Filesystem: in WP_Filesystem_FTPext::parselisting(), check for the existence of $b['islink'] before using it.

Props jesin.
Fixes #27975.


git-svn-id: https://develop.svn.wordpress.org/trunk@35476 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/class-wp-filesystem-ftpext.php

@@ -520,8 +520,9 @@ class WP_Filesystem_FTPext extends WP_Filesystem_Base {
 		}
 
 		// Replace symlinks formatted as "source -> target" with just the source name
-		if ( $b['islink'] )
+		if ( isset( $b['islink'] ) && $b['islink'] ) {
 			$b['name'] = preg_replace( '/(\s*->\s*.*)$/', '', $b['name'] );
+		}
 
 		return $b;
 	}