Update snippets fails with uninformative log error when snippets have already been downloaded

[galenbwill]

1. Uninstall plugin
2. Delete all snippets
3. Install plugin
4. Run update snippets from menu
5. Restart Binary Ninja
6. Verify snippets are visible in Snippets plugin menu
7. Run update snippets from menu
8. Observe failure in log:

[Default] Update failed.