ENH: Do not draw heatmap for leaves with no names.

When drawing the heatmap table for a tree, skip the
the rows for the leaves with no node names.

Change-Id: I4e54249070c2461cc473af717ffe617eb104b28c
Merge topic 'TreeHeatmapItemBug' into master

9377482f ENH: Do not draw heatmap for leaves with no names.