Removes unreachable stashes from a branch when no reachable have found

[sergeibbb]

Description

Solves #4353.

The problem was in incorrect handling of blank "reachable stashes" result. In some cases the set of unreachable wasn't cleared so undesired stashes and commits appeared in the view.

Checklist

• I have followed the guidelines in the Contributing document
• My changes follow the coding style of this project
• My changes build without any errors or warnings
• My changes have been formatted and linted
• My changes include any required corresponding changes to the documentation (including CHANGELOG.md and README.md)
• My changes have been rebased and squashed to the minimal number (typically 1) of relevant commits
• My changes have a descriptive commit message with a short title, including a Fixes $XXX - or Closes #XXX - prefix to auto-close the issue that your PR addresses