texlive-module.eclass: fix doc installation
If the package does not create ${WORKDIR}/texmf-doc, then the eclass assumes
that no documentation should be installed.
This is assumption is incorrect, since the documentation tar-balls can put the
docs into texmf-dist and not texmf-doc, as happens with e.g. texlive-mathscience.
As a result, the documentation files are not installed anymore.
Bug: https://bugs.gentoo.org/714908
Signed-off-by: Dominik Schmidt <dominik@schm1dt.ch>
Closes: https://github.com/gentoo/gentoo/pull/15128
Signed-off-by: Mikle Kolyada <zlogene@gentoo.org>