#167 3d axes: log sampling for xmode=log,ymode=log does not work

[Christian Feuersänger]

3d axes support logarithmic sampling in plot expression, but only in one direction. Please implement for both at once as well.

See also https://sourceforge.net/p/pgfplots/bugs/154/

\documentclass{article}
\usepackage{pgfplots}
\pgfplotsset{
compat=1.15,
}
\begin{document}

\begin{tikzpicture}
    \begin{axis}[
        only marks,
        domain=1:100,
        samples=21,
        samples y=21,
        xmode=log,
        ymode=log,
    ]
        \addplot3 {1};
    \end{axis}
\end{tikzpicture}

\end{document}