/usr/share/doc/libmgl-fltk7.5.0/changelog.Debian.gz is in libmgl-fltk7.5.0 2.4.1-2build2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libmgl-fltk7.5.0/../libmgl7.5.0/changelog.Debian.gz