iOS: only show menu if the control got active focus

If the control looses active focus, we start a timer
to update menu visibility. But when the timer fires
and we do the actual update, we didn't test for
active focus, which meant that we would show the
menu when we really meant to close it.

Change-Id: I6881e62be3a6cf4d82489663bc6d848d1dcf57d2
Reviewed-by: J-P Nurmi <jpnurmi@theqtcompany.com>