Fix error handling in OpenProcess wrappers.

Fix error handling in OpenProcess wrappers. 
OpenProcess returns NULL on error, see http://msdn.microsoft.com/en-us/library/windows/desktop/ms684320(v=vs.85).aspx

BUG= none
TEST= none

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=126717

[brettw, 2012-03-14 16:59:25]

lgtm

[commit-bot: I haz the power, 2012-03-14 17:36:37]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/halyavin@google.com/9703019/1

[commit-bot: I haz the power, 2012-03-14 20:24:45]

Change committed as 126717