fixes #3340

Set by default the maxValue of the chart to 0.0 when this one is null or negative.

msi.gama.core/src/msi/gama/outputs/layers/charts/ChartJFreeChartOutputRadar.java

@@ -102,7 +102,7 @@ protected AbstractRenderer createRenderer(final IScope scope, final String serie
 	 */
 	protected void resetRenderer(final IScope scope, final String serieid) {
 		final SpiderWebPlot plot = (SpiderWebPlot) this.chart.getPlot();
-
+		if (plot.getMaxValue() <= 0.0) plot.setMaxValue(1.0);
 		final ChartDataSeries myserie = this.getChartdataset().getDataSeries(scope, serieid);
 		if (!IdPosition.containsKey(serieid)) {
 			// DEBUG.LOG("pb!!!");