When launching as a thunderbird extension, with the -calendar argument

the resize function sometimes gets called before gCalendarWindow has been
initiated causing it not to work. This change should fix the problem.

calendar/resources/content/calendarWindow.js

@@ -580,7 +580,8 @@ CalendarWindow.prototype.onMouseUpCalendarViewSplitter = function calWinOnMouseU
 *   The resize handler, used to set the size of the views so they fit the screen.
 */
  window.onresize = CalendarWindow.prototype.doResize = function calWin_doResize(){
-     gCalendarWindow.currentView.refresh();
+  if( gCalendarWindow )
+    gCalendarWindow.currentView.refresh();
 }