include: Avoid overflow (warning) in RGBA_MAKE.

[Gerald Pfeifer]

On Sun, 26 Feb 2017, Henri Verbeet wrote:
>>>>> -#define RGBA_MAKE(r, g, b, a)   ((D3DCOLOR) (((a) << 24) | ((r) << 16) | ((g) << 8) | (b)))
>>>>> +#define RGBA_MAKE(r, g, b, a)   ((D3DCOLOR) (((unsigned)(a) << 24) | ((r) << 16) | ((g) << 8) | (b)))
> Commit 060ea15ae2c1604d51d3df1460e99c7d6e6211cf should have avoided the 
> issue.

Yes, indeed, that looks like it.  Thank you, Henri!

Gerald