And restore the possibility for the Polyhedron demo to load two types of C3t3 (with `Patch_id` being `int` or `std::pair<int, int>`).
Fixes a compilation error from clang: include/CGAL/IO/File_binary_mesh_3.h:39:10: error: no viable conversion from 'std::ostream' (aka 'basic_ostream<char>') to 'bool' return os << c3t3; ^~~~~~~~~~