Crash when try to add a Dropbox account

[andriykrefer]

Describe the bug
Crash when try to add Dropbox account

To Reproduce
Steps to reproduce the behavior:

1. Click on 'Add'
2. Click on 'Dropbox'
3. See error

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

Environment:

• OS and Version: Windows 10
• KeePass-Version: 2.57.1
• KeeAnywhere-Version: 2.1.0

Additional context
See the end of this message for details on invoking
just-in-time (JIT) debugging instead of this dialog box.

************** Exception Text **************
System.Exception: No unused port found!
at KeeAnywhere.OAuth2.OidcSystemBrowser..ctor(IEnumerable`1 ports)
at KeeAnywhere.StorageProviders.Dropbox.DropboxStorageConfigurator.d__1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at KeeAnywhere.StorageProviders.StorageService.d__9.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at KeeAnywhere.UIService.d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at KeeAnywhere.Forms.SettingsForm.d__a.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()