fix assert I added to KeyCode

in commit 9044260c35b22aeb6
"add some asserts to validate KeyCode values"

Change-Id: I73dc4c9ee5e4ced699d44ecdfb306a49b853f67e
Reviewed-on: https://gerrit.libreoffice.org/12180
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>
Tested-by: Noel Grandin <noelgrandin@gmail.com>