Allow GetScriptNameOrSourceURL to be called with exception pending.

R=jarin@chromium.org, ishell@chromium.org

Review URL: https://codereview.chromium.org/235943006

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20705 ce2b1a6d-e550-0410-aec6-3dcde31c8c00