libsrc/geom2d/csg2d.cpp:1736: Wpessimizing-move

[dcb314]

Recent development versions of gcc can be made to say:

/home/dcb36/rpmbuild/BUILD/netgen-6.2.2105/libsrc/geom2d/csg2d.cpp:1736:19: warning: moving a local object in a return statement prevents copy elision [-Wpessimizing-move]

Source code is

return std::move(res);

If the code is rewritten, then it might run a bit faster.