Contact Form: Provide default value when no "from" value is discernable.

### Impacted plugin

Jetpack

### What

Provide a fallback when name, e-mail, and IP address is not available for the "new" inbox.

### How

Originally reported in https://github.com/Automattic/jetpack/pull/39395#pullrequestreview-2307224483

In #39395, we added a filter to allow IP addresses to be excluded from the contact form results. The IP address is the final fallback in the contact form submission list for the "from" column if name/e-mail is not present. If the IP address is also not present, a blank appears for that entry.

Review the context from PR #39395, then locate the Jetpack contact form submission list for the new inbox and its "from" value handling. Confirm how name, e-mail, and IP address are selected, and make the issue done when an entry displays a fallback instead of a blank when all three are unavailable.

Written by the indexing model from the issue text.