Freeciv

I have an alien ruleset autogame crash in main branch, which I've debugged long enough to know that unit_make_contact() is being called for a dead unit (and at this time utype pointer within unit structure is garbage)
The crash happens in 'unit_has_type_flag(punit, UTYF_FLAGLESS)' call only present in S3_3 and main, but unit_make_contact() has also other unit pointer usages that are not correct with a dead unit.