fix for division by zero (rare cases)

htroot/NetworkHistory.java

@@ -123,10 +123,10 @@ public class NetworkHistory {
         if (columns.contains("cI")) headline = "YACY PEER '" + sb.peers.myName() + "' INDEX SIZE HISTORY: NUMBER OF DOCUMENTS";
         if (columns.contains("cR")) headline = "YACY PEER '" + sb.peers.myName() + "' INDEX SIZE HISTORY: NUMBER OF RWI ENTRIES";
         ChartPlotter chart = new ChartPlotter(width, height, 0xFFFFFFl, 0x000000l, 0xAAAAAAl, leftborder, rightborder, topborder, bottomborder, headline, "IN THE LAST " + timestr);
-        int pixelperscale = hspace / (maxtime / bottomscale);
-        if (pixelperscale > 0) chart.declareDimension(ChartPlotter.DIMENSION_BOTTOM, bottomscale, pixelperscale, -maxtime, 0x000000l, 0xCCCCCCl, "TIME/HOURS");
-        pixelperscale = 10 * ((vspace * leftscale / (maxpeers - minpeers)) / 10);
-        if (pixelperscale > 0) chart.declareDimension(ChartPlotter.DIMENSION_LEFT, leftscale, pixelperscale, minpeers, 0x008800l, null , columns.contains("cI") ? "DOCUMENTS" : columns.contains("cR") ? "RWIs" : "PEERS");
+        int pixelperscale = Math.max(1, hspace / (maxtime / bottomscale));
+        chart.declareDimension(ChartPlotter.DIMENSION_BOTTOM, bottomscale, pixelperscale, -maxtime, 0x000000l, 0xCCCCCCl, "TIME/HOURS");
+        pixelperscale = Math.max(1, 10 * ((vspace * leftscale / (maxpeers - minpeers)) / 10));
+        chart.declareDimension(ChartPlotter.DIMENSION_LEFT, leftscale, pixelperscale, minpeers, 0x008800l, null , columns.contains("cI") ? "DOCUMENTS" : columns.contains("cR") ? "RWIs" : "PEERS");
         
         // write the data
         float x0, x1;

source/net/yacy/visualization/ChartPlotter.java

@@ -102,6 +102,7 @@ public class ChartPlotter extends RasterPlotter {
 
     public void chartDot(final int dimension_x, final int dimension_y, final float coord_x, final int coord_y, final int dotsize, final String anot, final int anotAngle) {
         final int x = (int) ((coord_x - this.offsets[dimension_x]) * this.pixels[dimension_x] / this.scales[dimension_x]);
+        assert this.scales[dimension_y] != 0;
         final int y = (coord_y - this.offsets[dimension_y]) * this.pixels[dimension_y] / this.scales[dimension_y];
         if (dotsize == 1) plot(this.leftborder + x, this.height - this.bottomborder - y, 100);
                       else dot(this.leftborder + x, this.height - this.bottomborder - y, dotsize, true, 100);