[GiNaC-list] Potential issue in comparator in test_antipode

[Yuri Gribov]

Hi,

The comparison in `node::operator<` in time_antipode.cpp seems to be
missing a dereference operation in return statement:
  if (!(*vert==*n.vert))
    return (vert<n.vert);

This causes the comparator to be non-transitive:
  (gdb) p *keys[5] < *keys[4]
  $5 = true
  (gdb) p *keys[4] < *keys[8]
  $6 = true
  (gdb) p *keys[5] < *keys[8]
  $7 = false
which violates the strict weak ordering requirements of std::map
(https://en.cppreference.com/w/cpp/named_req/Compare). Such violations
may in practice result in non-deterministic behavior or crashes.

The issue was found with [SortChecker++
tool](https://github.com/yugr/sortcheckxx).

Best regards,
Yuri Gribov