Multiple close confirmation handlers

[FarSeeing]

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• I agree to follow the Code of Conduct that this project adheres to.
• I have searched the issue tracker for a feature request that matches the one I want to file, without success.

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Describe the bug
When closing a main window several times the confirmation modal is shown multiple times.

To Reproduce
Steps to reproduce the behavior:

1. Open the app
2. Open or create a new diagram
3. Modify that diagram
4. Close the main window by clicking the close button several times
5. If you're the fastest hand on the Wild West fast enough - the confirmation modal would be shown multiple times

Expected behavior
Confirmation modal is shown once

Screenshots
If applicable, add screenshots to help explain your problem.

draw.io version (In the Help->About menu of the draw.io editor):

• draw.io version 24.7.17

Desktop (please complete the following information):

• OS: Windows, MacOS, Linux...

Additional context
There is a check to display modal once by adding a unique id to each close handler but it doesn't work.
The lifecycle is close event - isModified-result - another close - another isModified-result so this unique id passes the check.

A proposal solution

index 76fa3e8..a59fa7f 100644
--- a/src/main/electron.js
+++ b/src/main/electron.js
@@ -269,11 +269,13 @@ function createWindow (opt = {})
                mainWindow.webContents.send('resize')
        });
 
-       let uniqueIsModifiedId;
+       let isModifiedInProgress;
 
        ipcMain.on('isModified-result', async (e, data) =>
        {
-               if (!validateSender(e.senderFrame) || uniqueIsModifiedId != data.uniqueId) return null;
+               if (!validateSender(e.senderFrame)) return null;
+
+               isModifiedInProgress = true;
 
                if (data.isModified)
                {
@@ -316,23 +318,29 @@ function createWindow (opt = {})
                {
                        mainWindow.destroy();
                }
+
+               isModifiedInProgress = false;
        });
 
        mainWindow.on('close', (event) =>
        {
-               uniqueIsModifiedId = Math.random().toString(36).substring(2, 15) + Math.random().toString(36).substring(2, 15);
-
                if (__DEV__)
                {
                        const index = windowsRegistry.indexOf(mainWindow)
-                       console.log('Window on close', index, uniqueIsModifiedId)
+                       console.log('Window on close', index, isModifiedInProgress)
+               }
+
+               if (isModifiedInProgress)
+               {
+                       event.preventDefault();
+                       return;
                }
 
                const contents = mainWindow.webContents
 
                if (contents != null)
                {
-                       contents.send('isModified', uniqueI
- sModifiedId);
+                       contents.send('isModified');
                        event.preventDefault();
                }

And a sidenote that the close even handler should probably handle a case when window contents have not loaded the JS (because of a CSP error maybe) and thus cannot reply with a isModified-result event.