[desktop_webview_window] Closes entire app when webview closes on Linux

When closing a webview on linux, it closes the entire app as well.

Reproduce Steps

Steps to reproduce the behavior:

1. Open a webview
2. Close the webview
3. Entire app closes

Expected behavior

The webview should close and the app should stay open

Version (please complete the following information):

• Flutter Version: 3.35.4
• OS: Linux
• plugin: [desktop_webview_window: 0.2.3]

Additional context

I've somewhat tracked down what is causing the issue, but I'm not sure the best approach to fix it.

When the webview window initializes the flutter view it eventually registers this callback to unrealize_cb here which is received when the window closes. I think this is shared with the main flutter application, and causes this error.

(webview_window_example:63441): Gdk-ERROR **: 21:38:39.941: The program 'webview_window_example' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadAccess (attempt to access private resource denied)'.
  (Details: serial 12779 error_code 10 request_code 152 (GLX) minor_code 26)
  (Note to programmers: normally, X errors are reported asynchronously;
   that is, you will receive the error a while after causing it.
   To debug your program, run it with the GDK_SYNCHRONIZE environment
   variable to change this behavior. You can then get a meaningful
   backtrace from your debugger if you break on the gdk_x_error() function.)
Lost connection to device.

Stack trace, showing the issue coming from unrealize_cb

#0  0x00007ffff40ba8d0 in _XError () at /lib/x86_64-linux-gnu/libX11.so.6
#1  0x00007fffdc05fc06 in  () at /lib/x86_64-linux-gnu/libGLX_mesa.so.0
#2  0x00007fffdc05fa92 in  () at /lib/x86_64-linux-gnu/libGLX_mesa.so.0
#3  0x00007fffe7125492 in  () at /lib/x86_64-linux-gnu/libGLX.so.0
#4  0x00007fffe7127813 in  () at /lib/x86_64-linux-gnu/libGLX.so.0
#5  0x00007fffe712c277 in  () at /lib/x86_64-linux-gnu/libGLX.so.0
#6  0x00007ffff576de7b in  () at /lib/x86_64-linux-gnu/libgdk-3.so.0
#7  0x00007ffff5738fd3 in gdk_gl_context_make_current () at /lib/x86_64-linux-gnu/libgdk-3.so.0
#8  0x00007ffff7155057 in unrealize_cb(_FlView*) ()

Just commenting out the lines that setup the flutter view allows the webview to close without taking the rest of the app with it. I haven't been able to find any way to keep it working while also setting up the flutter view

Here is the simple patch im using at the moment to work around the issue
https://github.com/MixinNetwork/flutter-plugins/compare/main...commetchat:mixin-flutter-plugins:webview-patch

Reproduce the Linux failure with packages/desktop_webview_window/linux/webview_window.cc, starting at the Flutter view setup around line 131 and the linked Flutter engine fl_view.cc unrealize_cb path. Compare the reported workaround, then verify that closing the webview no longer closes the main app or produces the shown GLX error.