Does the attached patch solve it for you too?
Attached emergency fix patch stops the crashing. Will push immediately.
I suspect this is not entirely correct fix (should we use the tile city is on when target_city is set instead of target_city?), so leaving the ticket open for the proper fix at later date.
I tried to run set of autogames on S3_1 (ce2d33934c7e4f196701a591eb86974f0be986a8). All of them dumped core after a couple of minutes.