Windows: Do not try to update keymap on WM_IME_CHAR messages

Task-number: QTBUG-35806

Change-Id: Ie1082353155aa7ee61f49f2fbcbfdb01d57e797c
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
(cherry picked from commit 0c09d2ccb9b46138a908950d65a49aa58dd55062)