AlphaBlend crashing msn messenger

[Maarten Lankhorst]

Fix AlphaBlend() to extract the right part of the source DIB.
(http://www.winehq.com/hypermail/wine-patches/2005/08/0331.html)

After some regression testing, It looks like this patch is the one
that breaks signing into msn messenger. I m not sure why, so Im
interested in finding out why it happens. I tried it with MSN
Messenger 6.2.0208, everything works ok until I try to sign in, then
it crashes with an error message like this:

trace:bitblt:GdiAlphaBlend 0x3b80 0,0 485x422 -> 0xa480 0,0 83x62
op=00 flags=00 srcconstalpha=ff alphafmt=01
err:syslevel:_CheckNotSysLevel Holding lock 0x404f0340 level 3
wine: Unhandled exception (thread 0009), starting debugger...

Without your patch, MSN signs in properly.