Tables not containing table header panic

[kokoISnoTarget]

When loading a file containing a table without a table header, the renderer will panic here: https://github.com/Inlyne-Project/inlyne/blob/15e7d498c6c1c952b05e66714def307e1a45e5d7/src/renderer.rs#L402C1-L402C75.

<table><th></th></table> // works

<table></table> // panics

Crash report produced by inlyne:
https://gist.github.com/kokoISnoTarget/6744e4501e67877f6c8c3a3be98c6e7c