wined3d: ActivateContext: try to fix wrong parameter?

[Rico Schüller]

Stefan Dösinger wrote:
> What happens if e.g. the current render target is an offscreen target and the 
> application tries to read back the front or back buffer? In this case you'll 
> read the offscreen target back.
> 
> So I am not sure this patch is correct

I have no idea I just tried a bit around and got cod4 
(http://bugs.winehq.org/show_bug.cgi?id=11584) working again with this 
patch.

I didn't step deep into this problem. So if I could help with some logs 
or other things, please let me know. Properly, the real bug is somewhere 
else?

Cheers
Rico