wined3d: Use a safer, more compliant method to parse extension strings

[Vitaliy Margolen]

Chris Robinson wrote:
> 
> +
> +    /* End */
> +    {NULL, 0}
>  };
[..]
> -            for (i = 0; i < (sizeof(EXTENSION_MAP) / sizeof(*EXTENSION_MAP)); ++i) {
> +            for (i = 0; EXTENSION_MAP[i].extension_string; ++i) {

What was the reason for this change? It's a static const array why do you 
want to treat it as a dynamically sized one?

Vitaliy.