[luatex] delimiter stretching broken in 0.89.3

[David Carlisle]

The following plain tex document

$$
n \choose l
$$
\bye

worked in 0.80 as in pdftex. I'm not sure quite which version it broke
at but in 0.89.3 it produces

This is LuaTeX, Version beta-0.89.3 (TeX Live 2016)
 restricted system commands enabled.
(./sp.tex
Overfull \vbox (15749.96411pt too high) has occurred while \output is active

and the brackets expand vertically for more than the page height.

David