/usr/lib/x86_64-linux-gnu/libqtcurve-cairo.so.1 is in gtk2-engines-qtcurve 1.8.18+git20160320-3d8622c-5build4.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libqtcurve-cairo.so.1.0