Fix js error when no visible items exist
Fix js error when no visible items exist

This prevents a js error where offset() returns null.

Fixes #2714

jensscherbl/symphony,jensscherbl/symphony,michael-e/symphony-2,bauhouse/sym-todo-list,symphonycms/symphony-2,bauhouse/sym-todo-list,symphonycms/symphony-2,michael-e/symphony-2