Fixes bug in Array.prototype.lastIndexOf when called with null or undefined as fromIndex argument. (fixes issue 754).

Review URL: http://codereview.chromium.org/2840021

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4950 ce2b1a6d-e550-0410-aec6-3dcde31c8c00