* Fixes#3959
There are two bugs racing each other here, which is why it sometimes
crashes and sometimes the app just silently exists
Bug 1
When the window is recreated a Destroyed event arrives (due to the Drop
of the old window). The code that receives this event does not look to
see if its the main viewport or a secondary one and unconditionally
closes the app. The code path for other platforms is slightly different
and does check.
I have moved the code that handles the destroy to be in the same place
and have the same behavior as the other platforms.
Bug 2
At recreate time the window and winit entries of the viewport are set to
None (forcin g them to be recreated). But the surface is still bound to
the old window, this causes the next context switch to fail. So I simply
added a viewport.gl_surface = None too,
This is my first egui PR so I hope I have not broken anything. If
nothing else I understand a little better how egui works.
0c528fb862