/usr/share/themes/Numix/unity/minimize_dash_disabled.svg is in numix-gtk-theme 2.6.7-3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/themes/Numix/unity/minimize_unfocused.svg
/usr/share/themes/Numix/unity/minimize_unfocused.svg