date_core.c: check conversion
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@62685 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
date_core.c: check conversion
conversion results, to get rid of infinite recursion.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@62685 b2dd03c8-39d4-4d8f-98ff-823fe69b080e