improving ScatterInspectorOverlay's handling of single-length and null-length selection lists
improving ScatterInspectorOverlay's handling of single-length and null-length selection lists

tommy-u/chaco,ContinuumIO/chaco,ContinuumIO/chaco,tommy-u/chaco,burnpanck/chaco,burnpanck/chaco,burnpanck/chaco,tommy-u/chaco,ContinuumIO/chaco,ContinuumIO/chaco