#6916 Fix notice during Update Bundle Product without changes

[dzianis-yurevich]

Description

If we need to update (not new) bundle product and edit any Bundle Items then the saving process works fine.
If we assign a new category and image to the product then the saving process doesn't work.

Fixed Issues

1. Update Bundle Product without changes in bundle items  #6916: Update Bundle Product without changes in bundle items

Manual testing scenarios

1. Edit sample product "Sprite Yoga Companion Kit"
2. by default this product has 4 options in bundle items. You need to add more so in total you have at least 21 options. And now we got Bundle Items pager.
3. Save product with all options and reload page.
4. Click save without any changes. you should see error.
5. If you move to the second page of bundle items and click save everything works correct.
   Looks like system think we trying to remove invisible items.

[magento-cicd2]

All committers have signed the CLA.

[ishakhsuvarov]

Hi @dzianis-yurevich
Please sign the CLA in the comment above so that we could proceed with the review and merge of your PR.
Thank you.

[dzianis-yurevich]

@ishakhsuvarov
CLA has been signed. Thank you!

[ishakhsuvarov]

@dzianis-yurevich Thank you

[ishakhsuvarov]

@dzianis-yurevich Do you think you could update

magento2/app/code/Magento/Bundle/Test/Unit/Controller/Adminhtml/Product/Initialization/Helper/Plugin/BundleTest.php

Line 10 in 4d4e88a

class BundleTest extends \PHPUnit\Framework\TestCase

to support this case?