[Bug 55192] New: user32:sysparams - test_SPI_SETWALLPAPER() fails to restore the '(None)' wallpaper

[WineHQ Bugzilla]

https://bugs.winehq.org/show_bug.cgi?id=55192

Bug ID: 55192
           Summary: user32:sysparams - test_SPI_SETWALLPAPER() fails to
                    restore the '(None)' wallpaper
           Product: Wine
           Version: unspecified
          Hardware: x86-64
                OS: Windows
            Status: NEW
          Severity: normal
          Priority: P2
         Component: user32
          Assignee: [e-mail]
          Reporter: [e-mail]

user32:sysparams - test_SPI_SETWALLPAPER() fails to restore the '(None)'
wallpaper:

sysparams.c:2442: Test failed: ***warning*** failed to restore the original
value: rc=0 err=2
sysparams.c:346: Test failed: Wrong value in registry: Control Panel\Desktop
Wallpaper '' instead of '(None)'

See https://test.winehq.org/data/patterns.html#user32:sysparams

Where 2 == ERROR_FILE_NOT_FOUND

This is systematic and specific to the w7u VM. The way I understand it that VM
does not have a wallpaper but instead of returning the like of an empty string,
SPI_GETDESKWALLPAPER returns '(None)' (maybe this is even the registry value).
Anyway when we try to restore the value, SPI_SETDESKWALLPAPER checks that the
'(None)' file exists and fails.

To investigate:
* Is '(None)' the actual registry value?
* Do our other VMs really all have a wallpaper? Is that why none of them
returns '(None)'?
* If another Windows version has no wallpaper does SPI_GETDESKWALLPAPER return
'None' or is that specific to Windows 7?
* To fix the test, check whether the oldvalue file exists and set the wallpaper
to an empty string if not? Or bypass SPI_SETDESKWALLPAPER to set the registry
directly in that case?