d3dx9: Fix D3DXPlaneNormalize on 64 bits.

[Henri Verbeet]

On 8 October 2010 16:32, Matteo Bruni <matteo.mystral at gmail.com> wrote:
> This patch changes D3DXPlaneNormalize to behave as native on 64 bits,
> returning infinity in the fourth plane component when the norm is 0.
> If this is not appropriate, I can resend without the implementation
> changes, just fixing the tests.
>
I can't say this is necessarily wrong, but I do think it looks suspicious.