fix: handle active storage preview error for password protected pdfs (#11888)

Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>

spec/models/attachment_spec.rb

@@ -68,6 +68,22 @@ RSpec.describe Attachment do
     end
   end
 
+  describe 'thumb_url' do
+    it 'returns empty string for non-image attachments' do
+      attachment = message.attachments.new(account_id: message.account_id, file_type: :file)
+      attachment.file.attach(io: StringIO.new('fake pdf'), filename: 'test.pdf', content_type: 'application/pdf')
+
+      expect(attachment.thumb_url).to eq('')
+    end
+
+    it 'generates thumb_url for image attachments' do
+      attachment = message.attachments.create!(account_id: message.account_id, file_type: :image)
+      attachment.file.attach(io: StringIO.new('fake image'), filename: 'test.jpg', content_type: 'image/jpeg')
+
+      expect(attachment.thumb_url).to be_present
+    end
+  end
+
   describe 'meta data handling' do
     let(:message) { create(:message) }