Pretty error message when post does not have an author

Replace the basic error message when a post does not have an author
with a nice looking error message page.

src/lua/endpoints/edit_post.lua

@@ -41,7 +41,16 @@ local function edit_post(req)
 	local err = util.do_sql(stmnt_author_of)
 	if err ~= sql.ROW then
 		stmnt_author_of:reset()
-		error("No author found for story:" .. storyid)
+		local msg = string.format("No author found for story: %d", storyid)
+		log(LOG_ERR,msg)
+		local response = pages.error{
+			errcode = 404,
+			errcodemsg = "Not Found",
+			explanation = msg,
+			should_traceback = true,
+		}
+		http_response(req,404,response)
+		return
 	end
 	local data = stmnt_author_of:get_values()
 	stmnt_author_of:reset()