Fix Vihko not remembering form contents when using a prefilled form

[mikkohei13]

Steps to reproduce

1. Go to https://laji.fi/vihko/templates
2. Click Käytä on a template
3. Add some data
4. Close the tab, ignoring the warning
5. Go to https://laji.fi/vihko/home

Actual Behaviour

On the sidebar, the form is not visible

Expected Behaviour

The form should be visible on the sidebar under "Tallentamattomat havaintoeräni"

Additional information

Firefox 151 on MmacOS Tahoe