fix timer tick error for Emacs 24.4

When in mpages mode but a different buffer, it was erroring on the void
variable by checking if true. boundp seems to be a valid fix. We shall
see.

mpages.el

@@ -77,7 +77,7 @@ Increasing this number may improve performance."
 (defun mpages-timer-tick ()
   "Run update on header with latest values."
   ;; this check makes sure it only runs update if the timer has been
-  (if mpages-count-timer
+  (if (boundp 'mpages-count-timer)
       (let ((word-count (count-words 1 (length (buffer-string))))
             (time-elapsed (time-subtract (current-time) mpages-start-time)))
         (mpages-update-word-count time-elapsed word-count))))