[Bug 55374] user32:msg - test_swp_paint_region_on_show() sometimes gets a NULLREGION on Windows 7

[WineHQ Bugzilla]

https://bugs.winehq.org/show_bug.cgi?id=55374

--- Comment #2 from François Gouget  ---
A very similar failure, unexpected NULLREGION, sometimes also happens in
test_swp_paint_region_on_extend_zerosize(). For instance on 2023-08-01 w7u-adm:

msg.c:9565: Test failed: GetRgnBox (on parent) returned 1
msg.c:9569: Test failed: parent update region: got (0,0)-(0,0), expected
(10,10)-(100,100)