RubyLB: Fix a crash on rewinding

We had a crash when breaking a ruby column again didn't shorten it.

Bug: 343749067
Change-Id: I505dd9af10c898f685edf708a60f1e9143d0ebdf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5610895


Commit-Queue: Koji Ishii <kojii@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Auto-Submit: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1312628}