Skip adding bots automatically when no NavMesh

[sunzenshen]

Description

• When no NavMesh is available for a map, skip auto-populating the server with bots.
• Bots can still be added manually with bot_add, though they will still be frozen.

Toolchain

• Windows MSVC VS2022

[sunzenshen]

Testing Ideas:

• Start a ntre_ map to verify that bots are still populated on maps with a NavMesh
• Start a legacy nt_ map to verify that bots are no longer populated automatically on maps without a NavMesh
• Use bot_add to force adding a bot on a map missing a NavMesh to verify that they can be spawned though frozen.

Warning message:

Forcing bot_add: