org-clock: Fix timezone in `org-clock-get-sum-start'

* lisp/org-clock.el (org-clock-get-sum-start): Remove timezone
  argument from `encode-time'.

Reported-by: Ihor Radchenko <ihor_radchenko@mymail.sutd.edu.sg>
<http://lists.gnu.org/r/emacs-orgmode/2017-12/msg00499.html>

lisp/org-clock.el

@@ -1456,8 +1456,7 @@ The time is always returned as UTC."
 	     (day (nth 3 dt)))
 	(if (< hour org-extend-today-until) (setf (nth 3 dt) (1- day)))
 	(setf (nth 2 dt) org-extend-today-until)
-	(setq dt (append (list 0 0) (nthcdr 2 dt) '(t)))
-	(apply #'encode-time dt)))
+	(apply #'encode-time (append (list 0 0) (nthcdr 2 dt)))))
      ((or (equal cmt "all")
 	  (and (or (not cmt) (equal cmt "auto"))
 	       (not lr)))