Crashes on lauch if syntax includes itself

Description of the problem or steps to reproduce

I tied to create my own python3 syntax highlight. In that I created some rules for python f-string. This is basically what I tried:

filetype: python3

...

rules:
    - constant.string:
        start: "f\""
        end: "\""
        rules:
            - formatstr:
                start: "{"
                end: "}"
                rules:
                    - include: "python3"

This lead to micro failing to launch next time I started it.

Specifications

You can use micro -version to get the commit hash.

Commit hash: 2c219ba
OS: Windows 10
Terminal: xterm-256color (WSL Ubuntu)

Start by reproducing the crash with the provided Python 3 syntax definition, especially the nested include of "python3", and inspect how micro loads syntax rules during launch. Done means micro can start normally even when a syntax definition includes itself, with the behavior covered by an appropriate regression test if the existing test structure supports it.