pythongh-98608: Fix Failure-handling in new_interpreter() (pythongh-1…

…02658)

The error-handling code in new_interpreter() has been broken for a while.  We hadn't noticed because those code mostly doesn't fail.  (I noticed while working on pythongh-101660.)  The problem is that we try to clear/delete the newly-created thread/interpreter using itself, which just failed.  The solution is to switch back to the calling thread state first.

python#98608

Python/pylifecycle.c

@@ -2062,10 +2062,10 @@ new_interpreter(PyThreadState **tstate_p, const _PyInterpreterConfig *config)
 
     /* Oops, it didn't work.  Undo it all. */
     PyErr_PrintEx(0);
+    PyThreadState_Swap(save_tstate);
     PyThreadState_Clear(tstate);
     PyThreadState_Delete(tstate);
     PyInterpreterState_Delete(interp);
-    PyThreadState_Swap(save_tstate);
 
     return status;
 }