Fix missing smi check in inlined indexOf/lastIndexOf.

BUG=382513
LOG=y
R=danno@chromium.org

Review URL: https://codereview.chromium.org/313233005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21727 ce2b1a6d-e550-0410-aec6-3dcde31c8c00