Fixes QKeyEvent::count() on Windows

All other main platform plugins leave the count parameter at its
default value (1). For improved compatibility, make the Windows plugin
do the same, instead of hardcoding the value to 0.

Task-number: QTBUG-31285
Change-Id: Id87fd559d13f42391be3200d5ff2393285f0d2a6
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Gatis Paeglis <gatis.paeglis@digia.com>