print only bar chart tics when they are greater than zero

pdb-plotting/src/main/java/org/lucares/pdb/plot/api/BarChartAggregatorForIntervals.java

@@ -134,6 +134,7 @@ public class BarChartAggregatorForIntervals implements CustomAggregator, Indexed
         int offset = 0;
         for (final String bucketId : bucketIds()) {
             final long count = buckets.get(bucketId).get();
+            if (count > 0) {
                 final String label = String.format(Locale.US, "set label at %s %f, %d '%s' center front offset 0,0.3\n", // front
                         xAxis == GnuplotAxis.X1 ? "first" : "second", //
                         offset + getIndex() * SPACE_BETWEEN_BARS + 0.5, // x-axis position of the label
@@ -141,6 +142,7 @@ public class BarChartAggregatorForIntervals implements CustomAggregator, Indexed
                         String.format(Locale.US, "%,d", count));
 
                 result.append(label);
+            }
             offset += numberOfDataSeries;
 
         }