HOME was checked but no check was made on whether or not the
result was NULL. This resolves issue #490 in the github issue
tracker.
Also: Modified the way that "select visible" works to check if
labels and/or cells are rendered visible in the window. If not,
then they are not selected. Previously, cell instances and
labels would be selected whether or not they were visible.
This resolves issue #503 in the github issue tracker.