Fix shutdown on foreign thread (#116233)

When a foreign thread running in .NET process is killed or crashes due
to some hardware exception, the .NET code that performs shutdown gets
called and incorrectly expects the thread to be a thread that's
registered with the runtime. It calls GetThread on it and then calls a
method on the thread. That leads to an assert in debug builds and crash
in release ones.

The function that is called is not needed for foreign threads though, so
the fix is to skip calling it if the GetThreadNULLOk returns NULL (that
means the thread is foreign and never registered with the runtime).

Co-authored-by: Jan Vorlicek <[email protected]>

Author: github-actions[bot]

src/coreclr/vm/ceemain.cpp

@@ -554,7 +554,11 @@ void EESocketCleanupHelper(bool isExecutingOnAltStack)
 
     if (isExecutingOnAltStack)
     {
-        GetThread()->SetExecutingOnAltStack();
+        Thread *pThread = GetThreadNULLOk();
+        if (pThread)
+        {
+             pThread->SetExecutingOnAltStack();
+        }
     }
 
     // Close the debugger transport socket first