Ensure Guard.groups doesn't fail when Guard has not been setup
Ensure Guard.groups doesn't fail when Guard has not been setup

There was an issue that could occur when instantiatin a
Guard plugin without setuping Guard itself (for instance in a
plugin test suite).

ginkel/guard,sdgdsffdsfff/guard,baberthal/guard,pjump/guard,sideci-sample/sideci-sample-guard,guard/guard,100star/guard,yujinakayama/guard,garettarrowood/guard