Fix method that ensures authentication token

Until now, `ensure_#{token_filed_name}` method didn't persist new token in database.

This closes #4235.

app/models/concerns/token_authenticatable.rb

@@ -17,12 +17,8 @@ module TokenAuthenticatable
       end
 
       define_method("ensure_#{token_field}") do
-        current_token = read_attribute(token_field)
-        if current_token.blank?
-          write_attribute(token_field, generate_token_for(token_field))
-        else
-          current_token
-        end
+        send("reset_#{token_field}!") if read_attribute(token_field).blank?
+        read_attribute(token_field)
       end
 
       define_method("reset_#{token_field}!") do

spec/models/concerns/token_authenticatable_spec.rb

@@ -35,6 +35,10 @@ describe ApplicationSetting, 'TokenAuthenticatable' do
 
         it { is_expected.to be_a String }
         it { is_expected.to_not be_blank }
+
+        it 'should persist new token' do
+          expect(subject).to eq described_class.current[token_field]
+        end
       end
     end