Fix a bug in graph construction for for loops.

A refactoring in SVN r24088 introduced a bug in for loops.  Loops with
continue in the body and an empty update expression list will lose the
edge from the continue to the loop entry.

R=fschneider@google.com
BUG=11375

Review URL: https://codereview.chromium.org//17491003

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@24214 260f80e4-7a28-3924-810f-c04153c831b5
2 files changed