wine: fix library path in wrapper when building without x11

This was caused by `MacOS::X11.lib` raising an exception because of the
`MacOS::X11#prefix` method: the `@prefix` instance variable stays nil
when neither `/opt/X11/lib/libpng.dylib` nor `/usr/X11/lib/libpng.dylib`
exist.

Closes #23640.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>