Visualize - redirect when field in URL is missing

To test:

- Create a visualization with a scripted field
- DO NOT SAVE, just apply and leave the app start as-is
- Rename or remove the scripted field
- Go back to Visualize

*Before this fix*

Page would fail silently and not load anything

*After this fix*

User sees an error at the top indicating that the field is missing, and is prompted to create a new visualization