Fix the correct removal of the images and the removal of all images in the catalog [Backport]

[raumatbel]

Related with the PR#11147
Fix the correct removal of the images and the removal of all images in the catalog

Description

When you want remove image from admin panel, this file is not removed correctly.
If the path of the image saved in the table catalog_product_entity_media_gallery is empty, this remove all the catalog.

Manual testing scenarios

For the first case.

1. Upload image from admin panel
2. Save product
3. Remove this image
4. Save product
   The file is not removed in pub/media/catalog/product/...

For the second case.

1. Upload image from admin panel
2. Save product
3. Go to the DB to the table catalog_product_entity_media_gallery and remove the value of this image
4. Remove this image from admin panel
5. Save product
   All the files are removed in pub/media/catalog/product/...

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[vkublytskyi]

@raumatbel Thank you for your contribution. We will merge your fixes to all branches shortly.

[ihor-sviziev]

Check "$isFile" is more faster, so would be great to swap them.

[raumatbel]

Can you explain me again? I don't understand well.
Do you want say me that I must not use the variable $isFile and I must specify it in the same line?.

   if (!($this->resourceModel->countImageUses($image['file']) > 1) && $this->mediaDirectory->isFile($this->mediaConfig->getBaseMediaPath() . $image['file']);) {

[vkublytskyi]

@raumatbel code if ($isFile && !($this->resourceModel->countImageUses($image['file']) > 1)) would be more optimal from performance perspective as if this is not a file then usage of image will not be checked.
I left up to you to make this fix or not as it may be considered as premature optimization. I think in code like this readability has higher priority.