Only migrate \@doendpe out of suitable groups

[FrankMittelbach]

Brief outline of the bug

The end \par handling after display environments done with \@doendpe has been changed recently to survive if the environment was placed in a group by checking the group level and using \aftergroup and retry after leaving the group. This was done always, but should have been done only in some groups. These are simple and semi-simple groups but not any of the 14 others.

In some groups, e.g., a \hbox group, there shouldn't be any display environments (but that should be tested upon starting the display environment not by the \@doendpe handling) in others, e.g., \vbox groups, it shouldn't happen at all, because the content of such boxes should not influence what happens after it. In normal LaTeX processing this isn't a problem, because on the document level things like minipage always start a paragraph and thus the paragraph continues after it, but in code that involves primitives like \vtop it can have undesirable side effects.

Minimal example showing the bug

\RequirePackage{latexbug}       % <--should be always the first line (see CONTRIBUTING)!
\documentclass{article}

\newcommand\sample{A text of more than a single line to see the paragraph indentation. Is this enough?}

\begin{document}

\sample

\vbox{\hsize=3cm\noindent \underline{Box content}}
\sample \space Should be indented.

\bigskip

\vbox{\hsize=3cm\noindent 
      \begin{itemize}\item \underline{Box content}\end{itemize}}
\sample Should be indented but isn't!

\sample

\end{document}

[FrankMittelbach]

hot fix has been distributed