Fixed PyRosetta build error
When compiling PyRosetta you could sometimes fail due to this error:
/suppscr/dimaio/danpf/git/Rosetta/master/source/src/protocols/floppy_tail/FloppyTailMover.cc:371:32: error: default initialization of an object of const type 'const std::set<core::Size>' (aka 'const set<unsigned long>') without a user-provided default constructor
std::set < core::Size > const empty; //easier to add empty sets to the vector than construct-then-add
This commit fixes that.