Fix fallback logic for code intel with extensions enabled

[sqs]

sourcegraph/sourcegraph-extension-api#59 (comment)

I have a repro:

1. Go to https://github.com/sourcegraph/sourcegraph-token-highlights/blob/master/src/extension.ts with "Use Sourcegraph extensions" on and with the URL set to https://sourcegraph.sgdev.org
2. Try hovering

You get 500s on everything, like:

POST https://sourcegraph.sgdev.org/.api/xlang/textDocument/definition 500

[sourcegraph-bot]

🎉 This issue has been resolved in version 1.15.0 🎉

The release is available on:

• Firefox Add-on
• Chrome Web Store
• npm package (@latest dist-tag)
• GitHub release

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