main: Close calendar on activateWindow()

If activateWindow() is called as the result of activating an item
in the Time & Date drop-down (most likely a notification), it should
behave as other items and close the calendar.

js/ui/main.js

@@ -529,6 +529,7 @@ function activateWindow(window, time, workspaceNum) {
     }
 
     overview.hide();
+    panel.closeCalendar();
 }
 
 // TODO - replace this timeout with some system to guess when the user might