org-timer: Fix `org-timer-stop'

* lisp/org-timer.el (org-timer-stop): Do not modify
  `org-timer-current-timer', which is related to countdown timer,
  a different feature.

lisp/org-timer.el

@@ -156,14 +156,12 @@ With prefix arg STOP, stop it entirely."
     (org-timer-set-mode-line 'pause)
     (message "Timer paused at %s" (org-timer-value-string)))))
 
-(defvar org-timer-current-timer nil)
 (defun org-timer-stop ()
   "Stop the relative timer."
   (interactive)
   (run-hooks 'org-timer-stop-hook)
   (setq org-timer-start-time nil
-	org-timer-pause-time nil
-	org-timer-current-timer nil)
+	org-timer-pause-time nil)
   (org-timer-set-mode-line 'off)
   (message "Timer stopped"))
 
@@ -349,6 +347,7 @@ VALUE can be `on', `off', or `pause'."
 	  (concat " <" (substring (org-timer-value-string) 0 -1) ">"))
     (force-mode-line-update)))
 
+(defvar org-timer-current-timer nil)
 (defun org-timer-cancel-timer ()
   "Cancel the current timer."
   (interactive)