Clean up.

slock.c

@@ -903,6 +903,8 @@ run_loop(struct arena *arena,
                             XResizeWindow(dpy, locks[screen]->win,
                                           rre->width, rre->height);
                         }
+                        XSetWindowBackground(dpy, locks[screen]->win,
+                                             BlackPixel(dpy, screen));
                         XClearWindow(dpy, locks[screen]->win);
                         break;
                     }