Workaround bug where events are received incorrectly
Workaround bug where events are received incorrectly

For some reason SDL passes events to us that occurred before we
gained focus, and passes them *after* the focus gained event.
Due to behavioural quirks from such events, whenever we gain focus
we have to clear the event queue. It's hacky, but works without
any visible side effects.

autrimpo/imv,eXeC64/imv,autrimpo/imv,eXeC64/imv