ntdll: Fix leaking activation context when terminating via exit_thread(). (Valgrind).

dlls/kernel32/thread.c

@@ -150,7 +150,6 @@ HANDLE WINAPI OpenThread( DWORD dwDesiredAccess, BOOL bInheritHandle, DWORD dwTh
  */
 void WINAPI ExitThread( DWORD code ) /* [in] Exit code for this thread */
 {
-    RtlFreeThreadActivationContextStack();
     RtlExitUserThread( code );
 }
 

dlls/ntdll/thread.c

@@ -376,6 +376,7 @@ void exit_thread( int status )
     }
 
     LdrShutdownThread();
+    RtlFreeThreadActivationContextStack();
 
     pthread_sigmask( SIG_BLOCK, &server_block_set, NULL );