cont.c: Check ruby_current_thread
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@50679 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
cont.c: Check ruby_current_thread
[Fix GH-914]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@50679 b2dd03c8-39d4-4d8f-98ff-823fe69b080e