cont.c: fix up r59557 for !FIBER_USE_NATIVE
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@59562 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
cont.c: fix up r59557 for !FIBER_USE_NATIVE
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@59562 b2dd03c8-39d4-4d8f-98ff-823fe69b080e