/usr/lib/libadplug.so is in libadplug-dev 2.2.1+dfsg3-0.1ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/libadplug-2.2.1.so.0.0.0
/usr/lib/libadplug-2.2.1.so.0.0.0