Wait for all NPCs to finish talking before speaking next line

[art-from-the-machine]

Currently, NPCs wait until their currently voiceline has finished before starting the next voiceline. However, if another NPC in a multi-NPC is still talking, the next NPC doesn't wait to start speaking, causing them to talk over each other. NPCs need to wait for the currently speaking NPC to stop speaking, not just when they themself have finished speaking.