Fix zerobucket comments and visibility

Author: JonasKunz

libs/exponential-histogram/src/main/java/org/elasticsearch/exponentialhistogram/ZeroBucket.java

@@ -72,7 +72,7 @@ public ZeroBucket(double zeroThreshold, long count) {
  this.count = count;
  }
 
- ZeroBucket(long index, int scale, long count) {
+ private ZeroBucket(long index, int scale, long count) {
  assert index >= MIN_INDEX && index <= MAX_INDEX : "index must be in range [" + MIN_INDEX + ", " + MAX_INDEX + "]";
  assert scale >= MIN_SCALE && scale <= MAX_SCALE : "scale must be in range [" + MIN_SCALE + ", " + MAX_SCALE + "]";
  this.index = index;
@@ -82,9 +82,9 @@ public ZeroBucket(double zeroThreshold, long count) {
  }
 
  private ZeroBucket(double realThreshold, long index, int scale, long count) {
+ this.realThreshold = realThreshold;
  this.index = index;
  this.scale = scale;
- this.realThreshold = realThreshold; // compute lazily when needed
  this.count = count;
  }