[luatex] Core dump error

[Br. Samuel Springuel]

I'm having some problems using `\localleftbox` and `\localrightbox` in 
LuaTeX 1.10 (the TeX Live 2019 Pretest) and GregorioTeX.  In trying to 
diagnose this problem, I stripped things down to this simple test document:

```
\documentclass{article}

\begin{document}
Something
\localleftbox{Hello}
%\localrightbox{Goodbye} % This one will trigger the error too.

Something
\end{document}
```

This document complies just fine with 1.07 (which shipped with TeX Live 
2018).  With 1.10, however, I get a core dump:

```
This is LuaTeX, Version 1.10.0 (TeX Live 2019)
  restricted system commands enabled.
(./Untitled.tex
LaTeX2e <2018-12-01>

luaotfload | main : initialization completed in 0.107 seconds
(/usr/local/texlive/2019/texmf-dist/tex/latex/base/article.cls
Document Class: article 2018/09/03 v1.4i Standard LaTeX document class
(/usr/local/texlive/2019/texmf-dist/tex/latex/base/size10.clo)) 
(./Untitled.aux
)lualatex: ../../../texk/web2c/luatexdir/lang/texlang.c:972: 
hnj_hyphenation: Assertion `tail != 0' failed.
Aborted (core dumped)
```

Did something change in `\localleftbox` and `\localrightbox` which I 
should be aware of?

-- 
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Br. Samuel, OSB
(R. Padraic Springuel)
St. Anselm’s Abbey
4501 South Dakota Ave, NE
Washington, DC, 20017
202-269-2300
(c) 202-853-7036

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