tikz: fix uses of \pgfutil@switch

[muzimuzhi]

Motivation for this change

This PR fixes a problem introduced by 70f814b. See previous discussions in #970 (comment).

Examples for testing:

\documentclass{article}
\usepackage{tikz}

\begin{document}
% test "\tikz@handle"
% current: infinite loop
% expected: throws error
%   ! Package tikz Error: Giving up on this path. Did you forget a semicolon?.
\tikz \path x;
\end{document}

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calendar}

\begin{document}
% test "\tikz@lib@cal@handle"
% current: infinite loop
% expected: throws error
%   ! Package tikz Error: Giving up on this calendar.
\tikz \calendar x;
\end{document}

Checklist

Please check the boxes to explicitly state your agreement to these terms:

• Code changes are licensed under GPLv2 + LPPLv1.3c
• Documentation changes are licensed under FDLv1.2

[hmenke]

Please go ahead. Your first merge as maintainer. 🎉