AI sometimes makes demands to an already defeated player

[Gurken Khan]

Sometimes the AI tries to negotiate with a player that's already defeated: makes no sense.

See: ​PetraAI bot doesn't recognize defeat of competitor, it's trading with (11/Oct/22)

analysing the replay from the forum link above

11:40 `User` wants to become neutral with `Lysander`
11:40 `Lysander` wants `1000 Food`
11:50 `User` sends `Lysander` `1000 Food`
11:50 `User` becomes neutral with `Lysander`

30:00 `User` wants to become allied with `Lysander` 
30:00 `Lysander` wants `1000 Food`
30:00-31:00 `User` sends `Lysander` `400 Food` (and `200 Metal, 100 Wood`)
31:10 `User` resigns
32:10 `Lysander` wants the remaining `600 Food` (asking a private message)

to reproduce

• start a match with some AI's
• try to make an alliance, where the AI asks you for a tribute
• only send a part of the tribute
• get defeated, for example with cheat code exodia 1
• AI asks you in a private message, for the rest
  • Attaching minimal replay (~2min) commands.txt​

note

To see private messages from the AI when watching the replay:

1. either change the name in the user.cfg to the name of the player, whose private messages from the AI you would like to see or
2. change the name in the attached replay file

[Langbart]

• adding a way to reproduce the issue

[Langbart]

Name image macro correctly in description

[Freagarach]

In 27481:

Fix PetraAI requesting tribute from defeated player.

The requests weren't deleted, both from received and sent diplomacy requests.

Reported by @Obelix at ​https://wildfiregames.com/forum/topic/96576-petraai-bot-doesnt-recognize-defeat-of-competitor-its-trading-with.
Investigated by: @Langbart
Differential revision: ​https://code.wildfiregames.com/D4904
Comment by: @phosis
Fixes #6654