Merged r17620, r17621 into trunk branch.

Fix potential assertion failure in ConvertCase.

Fix potential assertion failure.

BUG=
R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/66513006

git-svn-id: https://v8.googlecode.com/svn/trunk@17623 ce2b1a6d-e550-0410-aec6-3dcde31c8c00