Bug 1089451 - Swiping down from top edge when utility tray is already op...

...en and it closes; quite opposite from gesture's movement
we can maybe add a small unit test like [1] too

[1] https://github.com/mozilla-b2g/gaia/blob/8ae6598f3ab7b0c34ac42a73083ddb74266affba/apps/system/test/unit/utility_tray_test.js#L395-400