[bug] claim mode can unclaim the last claim chunk

[hkkongou]

description:
When edit mode of a claim is enabled , if a player remove the last claim chunk, he cannot add more claim chunk because there is no chunk next to each other.
"Chunks in your claim must be next to each other!" is shown

i know this is because "enforce-adjacent-claim-chunks" is set to true

In this case, if the claim mode is not exit direct after the last claim chunk is removed, or the last claim chunk deletion is being prevented, it will cause confusion to the players.

steps:

1. make a claim with 1 chunk
2. open claim edit mode
3. remove the chunk
   ->claim mode is still enabled but nothing can do other than exit claim mode manually

possible solutions:

1. prevent last chunk in the claim being delete, and send a message to player
2. show a menu to ask player to confirm remove claim since it is the last chunk in the claim [recommended]
3. directly exit the claim mode and tell player "you have removed the last chunk, claim mode will be exit"