[Bug 44310] WritePrivateProfileString doesn't check for flush errors

https://bugs.winehq.org/show_bug.cgi?id=44310

--- Comment #20 from Omega Software  ---
Based on instructions from
https://wiki.winehq.org/Developer_FAQ#I_sent_a_patch.2C_but_it_got_ignored._...
I'm going to submit only the conformance test first, as my first attempt didn't
catch Julliard's attention.

Fabian, may I have your permission to put your name in Signed-off-by for this
part, along with mine? (the code is mostly yours after all)

Thanks