(Minor) Naval units moved to non-coastal city in peace agreement

version 1.0.1.383

When trading a city that has a naval unit sitting in it, it is moved to another city of its owner even if that city can't build naval units.

save attached, repro steps:
1. Observe trireme sitting in Tondibi
2. Contact Askia and set for peace in trade of Tondibi
3. Notice the trireme was moved to Taghaza

I can't say if there were another coastal city if the unit would be moved to that city.
Doesn't matter much because Askia is getting POUNDED

Suggested:
1) Move unit outside of border but still in water. if no tile available, destroy the unit.
2) Destroy the unit 1) sounds complicated.

I think it's good you posted this here. It's not unknown, I've seen pictures of the same thing in the screenshots thread, but it's good to have an example in the bugs thread.