IA import 500s if no publish_date

### Problem

### Evidence

### Reproducing the bug

Run:

```js
await fetch("https://openlibrary.org/api/import/ia?identifier=robinhood0000gilb_v2r5&require_marc=false&debug=true", {
"method": "POST",
});
```

* Expected behavior: It imports the record
* Actual behavior: It errors

### Context

- Browser (Chrome, Safari, Firefox, etc):
- OS (Windows, Mac, etc):
- Logged in (Y/N): Y
- Environment (prod, dev, local): prod

### Notes from this Issue's Lead

#### Proposal & constraints

#### Related files

#### Stakeholders

#### Instructions for Contributors

- Please [run these commands](https://github.com/internetarchive/openlibrary/wiki/Git-Cheat-Sheet#working-on-your-branch) to ensure your repository is up to date **before** [creating a new branch](https://github.com/internetarchive/openlibrary/wiki/Git-Cheat-Sheet#making-changes-and-creating-a-pull-request) to work on this issue and **each time after** pushing code to Github, because the pre-commit bot may add commits to your PRs upstream.