Packet 0x0090
Packet 0x0090: "npc click"
pre: HUMAN
post: SCRIPT, Packet 0x0080, Packet 0x00b4, Packet 0x00b6, Packet 0x00c0, Packet 0x00c4
Click on an NPC, to invoke its script/shop/message.
Error if already talking to an NPC or too far.
No error if clicking on a warp.
