do not dereference `current` outside guard condition

Summary:
if current can be null, then clearly the one if must be nested inside
the guard if lest it trips over the nullptr when calling `name()`.

Test Plan: builds

Reviewers: #plasma, apol

Reviewed By: apol

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D22404