Fix Type::Intersect to skip uninhabited bitsets

R=verwaest@chromium.org, bmeurer@chromium.org
BUG=chromium:357330
LOG=Y

Review URL: https://codereview.chromium.org/219333003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20366 ce2b1a6d-e550-0410-aec6-3dcde31c8c00