Header referenced image not rendered properly

[jpsim]

First off, thank you very much for this gem. It's been powering a Swift & Objective-C documentation generator for years, and I'm very grateful! 🙏

We recently ran into a bug where referenced images (as opposed to inlined) in a header element wouldn't be rendered properly. See this small example:

$ cat README.md      
# H1 ![logo1] ![logo2] [![logo3](https://example.com/logo3.svg)](https://example.com)

[logo1]: https://example.com/logo1.svg
[logo2]: https://example.com/logo2.svg
$ redcarpet --version
Redcarpet 3.4.0
$ redcarpet README.md
<h1>H1 <img src="https://example.com/logo1.svg" alt="logo1"> ![logo2] <a href="https://example.com"><img src="https://example.com/logo3.svg" alt="logo3"></a></h1>

In this case, logo1 and logo3 are properly rendered as HTML but not logo2. Any assistance in resolving this would be greatly appreciated!

Original report here: realm/jazzy#1040