[1/2] user32: fix FindWindowEx behavior if window name is an empty charachter

[Louis Lenders]

> I sent 2 patches that make your FindWindow() tests pass
> under Wine. Did you
> run the tests after your fix? They don't pass without
> patching explorer.

I ran the "user32_crosstest.exe win" in wine, and the tests passed fine for me then. 
"make test" in user32 gives me a whole flood of failures, can't use that :(


>Also your test has a typo in the comment, and probably the tests
> need to go into
> their own test function, and not hijack the message window
> tests.
>

I've resent the tests. Thanks for the review