refactor(api): update story query helper

it now filters out stories with nonexistent authors

lib/server/listQuerier.ts

@@ -2,7 +2,7 @@ import { Band } from "~/models/band"
 import { Challenge } from "~/models/challenges/gen"
 import { Story } from "~/models/stories"
 
-export default async function(query, context, limit?, sort?) {
+export default async function(query, context, limit?: number, sort?) {
 	query["chapters.hidden"] = false
 		if(context.currentUser) {
 			if(!query.author) query.author = {}
@@ -19,5 +19,5 @@ export default async function(query, context, limit?, sort?) {
 			.populate({path: "challenge", model: Challenge}).populate('author', 'username _id')
 			.limit(limit || Infinity)
 			.exec();
-		return stories
+		return stories.filter(a => a.author != null)
 }