It so happens that when releasing the control key prior to the main key (C-h, C-i, C-n,
...), the substituted keycode was continuously sent in a loop after that (even when
releasing said key). The workaround so far was to type any other key to stop the loop.
This commit fixes such behavior by resetting the substitution keycode sent when the ctrl
released situation conditional is detected (and that the substitution keycode was on).
