Even empty block intervals should be associated with a fragmentainer.

We need to visit the fragmentainer that a block lives in even if said block has
zero height. If we find a column set, don't perform initial bounds checking.

BUG=675943

Review-Url: https://codereview.chromium.org/2597633002
Cr-Commit-Position: refs/heads/master@{#440361}
2 files changed