Prevent segfault if file cannot be opened when --ll_prof is used.

TEST=

BUG=
R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/16107002

Patch from Dusan Milosavljevic <Dusan.Milosavljevic@rt-rk.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14889 ce2b1a6d-e550-0410-aec6-3dcde31c8c00