Set cursorVisible to false when im cursor length is 0.

Set cursorVisible to false when im cursor length is 0.

If the length of the QInputMethodEvent::Cursor attribute is 0 the
cursor is supposed to be hidden.  To ensure this and any other IM
state is reverted when the input method is reset send a empty
event to the editor when preedit is cancelled or removed and
count formatting or cursor changes when determining if the
input method is composing (i.e has state that needs to be reset).

Change-Id: Ifca69aa0c18776b1aef355ed6ae9aecc40b9d475
Reviewed-by: Yann Bodson <yann.bodson@nokia.com>