vertbars should issue a \par at the beginning

[FrankMittelbach]

Given that vertbars can only be used on whole paragraphs it makes no sense in my opinion to only issue a \par at the end but not at the beginning

\documentclass{article}

\usepackage{lipsum,vertbars}

\begin{document}
\lipsum[1] 
\begin{vertbar}
  This paragraph gets a vertical bar.
  And this part should only have one bar but in fact it gets two!
  \begin{vertbar}
    A nested environment!
  \end{vertbar}
  And here the outer bar should still continue, which it does.
\end{vertbar}
\lipsum[1]
\end{document}