Pasting same title in html/markdown causes output to be nested

This is an issue that was forwarded to me, but I'm able to reproduce.

If text/html and text/plain contain the same title, the output we return is nested.

Expected output: `[[Same](https://google.com/)](https://google.com)"`
Actual output: `[Same](https://google.com)`

Reproduction: https://codepen.io/tarngerine/pen/ZEZBEpy

Try pressing the `Copy` button on either of the examples and try pasting into any GitHub comment box.

Start with the linked CodePen reproduction and compare what happens when copying each example into a GitHub comment box. Trace the paste handling in the repository to identify why identical text/html and text/plain titles produce non-nested output; done means the reproduction returns the expected nested Markdown link.

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