Bugfix for _getProductCollection on a product page

[evgk]

The following code will fail if $this->setCategoryId puts a category-instance instead of a category ID:

            if ($this->getCategoryId()) {
                try {
                    $category = $this->categoryRepository->get($this->getCategoryId());
                } catch (NoSuchEntityException $e) {
                    $category = null;
                }

Since category-repository object's get call can't accept the category-instance as parameter, it should be a category ID. Suggested patch fixes this issue(and method's comment).

[ihor-sviziev]

@evgk would be great to cover this case with unit tests

[vrann]

@evgk can you please update the branch with the latest from the mainline? There is a merge conflict.

[magento-cicd2]

All committers have signed the CLA.

[okorshenko]

@evgk thank you for your contribution. Your Pull Request successfully merged to develop branch