Fix marker in no buffer error for task state change in an indirect buffer

* lisp/org-clock.el (org-clock-out-if-current): Fix marker in no buffer error
  for task state change in an indirect buffer

org-clock-out-when-current was enhanced in 098cf35 (Clock: Clock out
when done also in indirect buffers, 2009-03-23) to handle indirect
buffers.

This enhancement uses (buffer-base-buffer (org-clocking-buffer)) but
when not clocking (org-clocking-buffer) returns nil - so
buffer-base-buffer returns the base buffer of the current buffer which
is never nil.  This leads to marker in no buffer errors trying to stop
the clock when it is not running.

Now we explicitly check up front that the clock is running before
any other conditions that lead to stopping the clock.

lisp/org-clock.el

@@ -1696,7 +1696,8 @@ from the `before-change-functions' in the current buffer."
   "Clock out if the current entry contains the running clock.
 This is used to stop the clock after a TODO entry is marked DONE,
 and is only done if the variable `org-clock-out-when-done' is not nil."
-  (when (and org-clock-out-when-done
+  (when (and (org-clocking-p)
+	     org-clock-out-when-done
 	     (or (and (eq t org-clock-out-when-done)
 		      (member state org-done-keywords))
 		 (and (listp org-clock-out-when-done)