[Bug 38796] dwrite analyzer test crashes on my system

https://bugs.winehq.org/show_bug.cgi?id=38796

--- Comment #1 from Bernhard Übelacker  ---
In this test the call to create_fontface comes down to
systemfontfileenumerator_GetCurrentFontFile.

There it calls RegEnumValueW to enumerate the fonts in
HKLM\Software\Microsoft\Windows NT\CurrentVersion\Fonts.
With two calls, one for getting the required buffer length, one to retrieve
the content.

In my case the font "Tahoma Bold" has value which is 109 characters long.
(I probably have too many subdirectories and the value is generated
from drive Z:)

Unfortunately the first call to RegEnumValueW calls NtEnumerateValueKey just
with an fixed buffer and returns with a too low needed buffer size.

Then the second call to RegEnumValueW also fails with the too small buffer.

Attached patch changes RegEnumValueW to retrieve the correct needed buffer
size.