scripted_sequence can be broken by +using friendly NPCs to make them follow player

[SamVanheer]

If the player +uses a friendly NPC to make them follow the player right after a scripted_sequence has started then the NPC will instead try to treat the player as its target entity.

This results in the NPC either trying to move towards the player or, if the player has +used the NPC again to stop them following the player, causes the NPC to access a null pointer, crashing the game.

Originally reported by Oxofemple.