If the legend area is too small or has not enough space to render the
series title, it will be shortened (e.g. "Very Long Series Title" becomes
"Very Long S..."). Thus, the comparison will fail and there is no other
way to determine which series title is currently being rendered on the
legend area...
I think, there must be a hint given to beforeDrawLegendItem to be able to
determine the series; maybe an additional param with the series identifier
(beforeDrawLegendItem(..., Object seriedID ))...