Only avoid glow context switching on Windows

[emilk]

…since it is reportedly broken on Windows

• Early-out added in eframe: Early-out from context switching the glow backend #4284
• Re-opens eframe on Windows high CPU usage due to excessive calls to glutin::context::make_not_current #4173 😭
• Closes After the #4284 update, Viewport graphics are broken. #4289
• Closes The contents of #4284 have been reverted #4290

[emilk]

@rustbasic please test this

[YgorSouza]

FWIW I'm not seeing any problems with the test_viewports example on Linux, neither on this branch nor on master.

OS: Fedora Linux 39 (Workstation Edition) x86_64 
Host: Laptop (12th Gen Intel Core) A6 
Kernel: 6.7.10-200.fc39.x86_64 
Resolution: 2256x1504 
DE: GNOME 45.5 
WM: Mutter 
WM Theme: Adwaita 
Theme: Adwaita-dark [GTK2/3] 
Icons: Adwaita [GTK2/3] 
CPU: 12th Gen Intel i7-1260P (16) @ 4.700GHz 
GPU: Intel Alder Lake-P GT2 [Iris Xe Graphics] 
Memory: 7123MiB / 64008MiB 

[rustbasic]

@rustbasic please test this

As a result of a short test,
It's Normal.

If any other abnormalities are found, we will notify you again.

[rustbasic]

@YgorSouza

YgorSouza, what do you want to do in linux ?

return or not return ?

[emilk]

Thanks @YgorSouza - so sounds this is is a Windows-only problem then.

[YgorSouza]

By the way, I just noticed another problem with this example on Linux, but I think it is unrelated to this. When I alt+tab into and out of the application a few times, eventually the viewports start hanging. But I tried the commits that reverts the early return for linux and the one that doesn't, and it seems that both have the same problem.

[YgorSouza]

When I alt+tab into and out of the application a few times, eventually the viewports start hanging

And this also happens with the wgpu feature, so definitely not related to this PR. That's the only problem I found on Linux so far.