[FIX-716] Avoid fetching scope data to check if it is blank

[dalthon]

Address the issue raised here: #716

There was some unnecessary, possibly heavy, queries being done.

---

• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Added an entry to the changelog if the new code introduces user-observable changes. See changelog entry format for details.

[rabotyaga]

Let's follow the contributing guide:

If the change has a related GitHub issue (e.g. a bug fix for a reported issue), put a link to the issue as [#123](https://github.com/toptal/chewy/issues/123): 

• #716: Avoid fetching scope data to check if it is blank ([@dalthon][])