treeview: Don't show empty tooltips
If the column used for the GtkTreeView:tooltip-column contains NULL we're already skipping a tooltip; let's ignore empty strings as well, as an empty tooltip is pretty much pointless.
Close #1681 (closed)
If the column used for the GtkTreeView:tooltip-column contains NULL we're already skipping a tooltip; let's ignore empty strings as well, as an empty tooltip is pretty much pointless.
Close #1681 (closed)