fix(insights): fix broken download with invalid dates (#4769)

## Description

The download path wasn't checking for invalid dates like the UI was

## Release note

<!-- User-facing release note. Use "None" if this does not need release
notes. -->
None.

## Migration note

<!-- Upgrade, deployment, config, schema, or compatibility notes. Use
"None" if none. -->
None.

*[Check our Pull Request
Guidelines](https://github.com/inngest/inngest/blob/main/docs/PULL_REQUEST_GUIDELINES.md)*

Co-authored-by: Albert Chae <albertchae@users.noreply.github.com>