Added validity check when updating NPC state.

Fixed incompatibility with Nextbots due to alive state checking method.

Added a minimum distance where NPCs will always be visible to prevent them from popping in right around a corner at close range.

- Fixed Hunter flickering in death animation.
- Fixed default map fog not showing when ho_fog_enabled is set to 0.

- Fixed the case of "ghost model" appearing on NPC death.
- Made it so that all NPCs draw when ho_enabled turns to 0. This is to prevent invisible NPCs.

Removed line of sight optimization for rollermines until further notice.

Fixed floating weapon bug for Modern Warfare II - Takedowns & Revive System.