FIX: unable to filter user directory when sorted by user field. (#15951)

Since the "users" table is already added in the "includes" method it gives unexpected results while using it again in the "joins" method.

app/controllers/directory_items_controller.rb

@@ -38,7 +38,7 @@ class DirectoryItemsController < ApplicationController
       user_field = UserField.find_by(name: params[:order])
       if user_field
         result = result
-          .joins(:user)
+          .references(:user)
           .joins("LEFT OUTER JOIN user_custom_fields ON user_custom_fields.user_id = users.id AND user_custom_fields.name = 'user_field_#{user_field.id}'")
           .order("user_custom_fields.name = 'user_field_#{user_field.id}' ASC, user_custom_fields.value #{dir}")
       end

spec/requests/directory_items_controller_spec.rb

@@ -136,6 +136,41 @@ describe DirectoryItemsController do
       expect(json['directory_items'][1]['user']['username']).to eq(evil_trout.username) | eq(stage_user.username)
     end
 
+    it "orders users by user fields" do
+      group.add(walter_white)
+      field1 = Fabricate(:user_field, searchable: true)
+      field2 = Fabricate(:user_field, searchable: true)
+
+      user_fields = [
+        { user: walter_white, field: field1, value: "Yellow", order: 1 },
+        { user: stage_user, field: field1, value: "Apple", order: 0 },
+        { user: evil_trout, field: field2, value: "Moon", order: 2 }
+      ]
+
+      user_fields.each do |data|
+        UserCustomField.create!(
+          user_id: data[:user].id,
+          name: "user_field_#{data[:field].id}",
+          value: data[:value]
+        )
+      end
+
+      get '/directory_items.json', params: { period: 'all', group: group.name, order: field1.name, user_field_ids: "#{field1.id}|#{field2.id}", asc: true }
+      expect(response.status).to eq(200)
+
+      json = response.parsed_body
+      expect(json).to be_present
+      items = json['directory_items']
+      expect(items.length).to eq(3)
+      expect(json['meta']['total_rows_directory_items']).to eq(3)
+
+      user_fields.each do |data|
+        user = items[data[:order]]['user']
+        expect(user['username']).to eq(data[:user].username)
+        expect(user['user_fields']).to eq({ data[:field].id.to_s => data[:value] })
+      end
+    end
+
     it "checks group permissions" do
       group.update!(visibility_level: Group.visibility_levels[:members])