fix: check for destroyed webcontents in converter (#25431)

spec-main/fixtures/crash-cases/webview-attach-destroyed/index.js

@@ -0,0 +1,9 @@
+const { app, BrowserWindow } = require('electron');
+
+app.whenReady().then(() => {
+  const w = new BrowserWindow({ show: false, webPreferences: { webviewTag: true } });
+  w.loadURL('data:text/html,<webview src="data:text/html,hi"></webview>');
+  app.on('web-contents-created', () => {
+    w.close();
+  });
+});