fix: correctly handle if last header is empty in XHR interceptor

[porcellus]

Summary of change

fix: correctly handle if the last header is empty in the XHR interceptor

Related issues

• https://app.circleci.com/pipelines/github/supertokens/supertokens-golang/1457/workflows/ba9039ed-b47f-4bd1-bcd5-b883727c243f/jobs/349

Test Plan

The golang tests cover this, + I'll add testing this into my backlog

Documentation changes

N/A

Checklist for important updates

• [x] Changelog has been updated
• [x] frontendDriverInterfaceSupported.json file has been updated (if needed)
  • Along with the associated array in lib/ts/version.ts
• [x] Changes to the version if needed
  • In package.json
  • In package-lock.json
  • In lib/ts/version.ts
• [x] Had run npm run build-pretty
• [x] Had installed and ran the pre-commit hook
• [x] Issue this PR against the latest non released version branch.
  • To know which one it is, run find the latest released tag (git tag) in the format vX.Y.Z, and then find the latest branch (git branch --all) whose X.Y is greater than the latest released tag.
  • If no such branch exists, then create one from the latest released branch.

[github-actions[bot]]

size-limit report 📦

Path	Size
lib/build/bundleEntry.js	18.84 KB (+0.22% 🔺)