So check whether the name is actually set before printing it when
throwing an exception.

BUG=none
R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/23283011

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@16233 ce2b1a6d-e550-0410-aec6-3dcde31c8c00