Improve verification of new user as admin or user

packages/rocketchat-lib/server/models/Users.coffee

@@ -2,6 +2,8 @@ RocketChat.models.Users = new class extends RocketChat.models._Base
 	constructor: ->
 		@model = Meteor.users
 
+		@tryEnsureIndex { 'roles': 1 }, { sparse: 1 }
+
 
 	# FIND ONE
 	findOneById: (_id, options) ->

server/lib/accounts.coffee

@@ -83,11 +83,11 @@ Accounts.insertUserDoc = _.wrap Accounts.insertUserDoc, (insertUserDoc, options,
 
 	if roles.length is 0
 		# when inserting first user give them admin privileges otherwise make a regular user
-		firstUser = RocketChat.models.Users.findOne({ _id: { $ne: 'rocket.cat' }}, { sort: { createdAt: 1 }})
-		if firstUser?._id is _id
-			roles.push 'admin'
-		else
+		hasAdmin = RocketChat.models.Users.findOne({ roles: 'admin' }, {fields: {_id: 1}})
+		if hasAdmin?
 			roles.push 'user'
+		else
+			roles.push 'admin'
 
 	RocketChat.authz.addUserRoles(_id, roles)