comctl32/listview: fix calculating item height

[Daniel Jelinski]

Interesting:
https://testbot.winehq.org/JobDetails.pl?Key=23746&log_206=1#k206
Looks like testbot tried to do the entire test suite, even though I
changed only one test file.

2013/1/5 Marvin <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=23746
>
> Your paranoid android.
>
>
> === W2K8SE (32 bit listview) ===
> Failure running script in VM: The specified guest user must be logged in interactively to perform this operation