OpenWebstart get stuck on certificate selection screen (multi-threading with event dispatch thread hack)

I was able to reproduce this with a self-issued certificate on localhost.

The problem exists when doing a backend call in a SwingUtilities.invokeLater at the same time as a background thread calls a the backend to the server with a broken certificate.

Result: the certificate dialog and the UI are completely frozen.

Now it's super easy to reproduce, see my comment:
https://github.com/karakun/OpenWebStart/issues/594#issuecomment-2498960727

I suspect that the locking does not work properly in this case, in the following section:
https://github.com/AdoptOpenJDK/IcedTea-Web/blob/d8414248348bc2b08cb5f97926decaa491a0dfa8/core/src/main/java/net/adoptopenjdk/icedteaweb/client/parts/dialogs/security/SecurityDialogs.java#L305

``` awt thread
message.lock = null;
...

// background thread
message.lock = new Semaphore(0);
...
message.lock.acquire();
```
and most likely both call `JNLPRuntime.getSecurityDialogHandler().postMessage(message);`

btw this issue was first raised here: https://github.com/karakun/OpenWebStart/issues/594
but the broken code is in this repo (14 year old code ... :-))