Page dimension issue with wallpaper package

[jspitz]

(Moving over from reutenauer/polyglossia#48)

Page dimensions are off with wallpaper package and bidi. See MWE:

% !TeX TS-program = xelatex
\documentclass[a4paper]{book}%
\usepackage{wallpaper}
\usepackage{polyglossia}
\newfontfamily\arabicfont[Script=Arabic]{Amiri}
\setdefaultlanguage{arabic}
\begin{document}
test
\ThisCenterWallPaper{1}{hya.png}
\end{document}

with example image from here.

This might be related to #6.