Problem: When nvim is started with "-s -" (read from stdin), ":restart"
drops the "-" argument but keeps "-s", leaving an orphaned "-s" in the
restarted server's argv, causing a crash.
Solution: Drop "-s" and its scriptfile argument when copying v:argv for
the restarted server. Like "-- [files…]", the scriptfile is a one-shot
startup input that should not be replayed on restart