This fixes a corner case that happens when JSFunctions are enqueued as
code flushing candidates but their respective SharedFunctionInfo isn't.
If the JSFunction gets evicted due to optimization the code slot in the
SharedFunctionInfo will never be recorded in the slots buffer.
R=hpayer@chromium.org
BUG=chromium:168801
TEST=cctest/test-heap/Regress168801
Review URL: https://codereview.chromium.org/11896064
git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@13481 ce2b1a6d-e550-0410-aec6-3dcde31c8c00