Cover DataExtractor with a unit test

[sivaschenko]

Cover \Magento\MediaGallery\Model\DataExtractor with a unit test

[sivaschenko]

Hi @valentinboyanov are you working on this issue? Do you have any updates?

[sivaschenko]

Removed assignment as there is no response from the assignee. Ready for development.

[sivaschenko]

Hi @larsroettig are you working on this issue?)

[sivaschenko]

PR for this issue should target magento2 repository