windowscodecs: Implement IWICPalette_InitializeFromPalette.

[Vincent Povirk]

> +    EnterCriticalSection(&This->lock);
> +    This->colors = colors;
> +    This->count = count;
> +    This->type = type;
> +    LeaveCriticalSection(&This->lock);

You're leaking the previous value of This->colors.