fix: Referer URL validation (#4309)

Fixes #354

spec/models/conversation_spec.rb

@@ -525,4 +525,20 @@ RSpec.describe Conversation, type: :model do
       expect { notification.reload }.to raise_error ActiveRecord::RecordNotFound
     end
   end
+
+  describe 'validate invalid referer url' do
+    let(:conversation) { create(:conversation, additional_attributes: { referer: 'javascript' }) }
+
+    it 'returns nil' do
+      expect(conversation['additional_attributes']['referer']).to eq(nil)
+    end
+  end
+
+  describe 'validate valid referer url' do
+    let(:conversation) { create(:conversation, additional_attributes: { referer: 'https://www.chatwoot.com/' }) }
+
+    it 'returns nil' do
+      expect(conversation['additional_attributes']['referer']).to eq('https://www.chatwoot.com/')
+    end
+  end
 end