Fix error loading requests with empty header values from history

[LucasPickering]

Description

Describe the change. If there is an associated issue, please include the issue link (e.g. "Closes #xxx"). For UI changes, please also include screenshots.

Just a simple parsing bug. I assumed header values couldn't be empty, which is wrong. I DID confirm that empty header names are invalid (not allowed by the http crate) so don't need to worry about that.

Closes #400

Known Risks

What issues could potentially go wrong with this change? Is it a breaking change? What have you done to mitigate any potential risks?

This is a temporary fix. I'd love to use a library for the parsing, but it's not clear if I can tap into reqwest/hyper/httparse to do this, so I need to work on it a bit more.

QA

How did you test this?

Manually :(

Checklist

• Have you read CONTRIBUTING.md already?
• Did you update CHANGELOG.md?
  • Only user-facing changes belong in the changelog. Internal changes such as refactors should only be included if they'll impact users, e.g. via performance improvement.
• Did you remove all TODOs?
  • If there are unresolved issues, please open a follow-on issue and link to it in a comment so future work can be tracked