Fixes a regression introduced in
https://github.com/zed-industries/zed/issues/49603
Supersedes https://github.com/zed-industries/zed/pull/52638

We want to leave these non-existent workspaces in the database for up to
7 days, in case they are on external drives that are restored later, but
we do *not* want to show them in the UI if they don't exist.

Release Notes:

- Fixed an issue where deleted folders appeared in the recent project
picker

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Co-authored-by: ojpro <contact@ojpro.me>