Don't crash in Array.join() if the resulting string exceeds the max string length.

LOG=y
BUG=336820
R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/144533003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18986 ce2b1a6d-e550-0410-aec6-3dcde31c8c00