Fixes bug on conditional branch where the targets are the same.

Fixes constructor InstBr when it is a conditional branch, and the
true and false branches are the same.

BUG= https://code.google.com/p/nativeclient/issues/detail?id=4212
R=jpp@chromium.org, stichnot@chromium.org

Review URL: https://codereview.chromium.org/1215443002.
2 files changed