changes to actionchecker perms levels for file uinlinks, and reverse check for board exist in form

controllers/forms/deleteboard.js

@@ -28,7 +28,7 @@ module.exports = async (req, res, next) => {
 		} catch (err) {
 			return next(err);
 		}
-		if (board != null) {
+		if (!board) {
 			//global must check exists because the route skips Boards.exists middleware
 			errors.push(`Board /${req.body.uri}/ does not exist`);
 		}

helpers/checks/actionchecker.js

@@ -1,7 +1,7 @@
 'use strict';
 
 const actions = [
-	{name:'unlink_file', global:true, auth:3, passwords:true, build:true},
+	{name:'unlink_file', global:true, auth:4, passwords:true, build:true},
 	{name:'delete_file', global:true, auth:1, passwords:false, build:true},
 	{name:'spoiler', global:true, auth:4, passwords:true, build:true},
 	{name:'delete', global:true, auth:4, passwords:true, build:true},