NasalSys.cxx more robust instead. The reason for the crash was that during
fgfs shutdown destroyed subsystems (GENERAL group) still need Nasal access
(for AI Model destruction listeners), but at that point globals->get_subsystem()
can't even deliver the "nasal" subsystem (INIT group). One way to solve that
problem would have been to replace globals->get_subsystem("nasal") by
globals->get_subsystem_mgr()->get_group(SGSubsystemMgr::INIT)->get_subsystem("nasal"),
but Andy decided to store a pointer to the active "nasal" subsysten in
NasalSys.cxx instead, as the "nasal" subsystem needs to be accessed in
every single Nasal extension function, and multiple "nasal" subsystems are
out of the question, anyway.
we need to explicitly destroy that here, too, so that it has guaranteed
access to the Nasal subsystem. Otherwise we get a segfault on exit. When
the next subsystem needs this special treatement (radar?), we should
introduce a new subsystem group (in addition to INIT and GENERAL)
are taken down by the C++ runtime environment. This will later be done
with runlevels. Why would we want to run nasal code in subsystem
destructors? We don't really. But some data structures may use nasal,
which are normally created/destroyed during runtime. And these will
also be destroyed at fgfs exit. In the past things like these didn't
happen, because someone had disabled all subsystem destructors ...
explicit calls to shutdown_all() which was causing this to be called twice.
This could cause problems with some IO modules (such as attempting to close
an invalid file descriptor the second time.)
