05e0f20600
Triple click in side-by-side mode with other side empty results in DOM selection ending on the empty div line number tag. Normalizing such selection results in null element for the end container. This is handled on ad-hoc basis by validating where DOM selection landed and is handled properly. Previous fix (https://gerrit-review.googlesource.com/c/gerrit/+/193470) was only addressing the case when the other diff side is populated. Bug: Issue 8431 Change-Id: I17964db98c217d30dd266e01d0a03a11ed9c42b9