Always deoptimize on undefined if a double value implicitly gets converted.

R=svenpanne@chromium.org

Review URL: https://chromiumcodereview.appspot.com/16126002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14832 ce2b1a6d-e550-0410-aec6-3dcde31c8c00