Fixing bug where mouse resets when leaving window

When moving the mouse outside, it is reset to 0,0 and when alt tabbing some high value garbage numbers were sent. This missing break was the cause, because WINDOWEVENT was being handled and pumped by MOUSEMOTION as well. *smh*

Fixes https://github.com/openfl/openfl-native/issues/162 for sure, possibly other mouse/window related issues.

Let's test any mouse related issues against this?