comctl32/treeview: Make item data layout partially compatible with native one

[testbot at testbot.winehq.org]

Hi,

While running your changed tests on Windows, I think I found new failures.
Being a bot and all I'm not very good at pattern recognition, so I might be
wrong, but could you please double-check?
Full results can be found at
http://testbot.winehq.org/JobDetails.pl?Key=6609

Your paranoid android.


=== WNT4WSSP6 (32 bit treeview) ===
No test summary line found

=== W2KPROSP4 (32 bit treeview) ===
No test summary line found