Abort glyph rendering if everything is clipped

[Warren_Baird at cimmetry.com]

> That looks better yes; it's still a bit complex IMO, but I'm not sure
> it's possible to do much better with that glyph index thing. Still I'm
> wondering if you shouldn't do the IsRectEmpty check after the LPtoDP
> and coordinates swap.

It looks to me like LPtoDP is just doing a linear transform, so the area should
be preserved - the rectangle should be empty after the transform if and only if
it is empty before the transform.

Or am I missing something?  Is there another reason to move the IsRectEmpty
check after the transform?

Warren