e_service_launcher: fix frame sync issue in case launcher is widget

e_service_launcher: fix frame sync issue in case launcher is widget

It is possible that previous frame of backward effect is shown by widget viewer window
even if showing of launcher client is pending until after prepare event is sent and
launcher client attach buffer, because pre visibility and iconify changed event is sent
to widget viewer before prepare event is sent to launcher client.
so this patch grap uniconify job of widget viewer until widget viewer attach buffer
between backward effect launching and done.

Change-Id: Ib7c868da83021cd0ceb970181f543b0d33005014