[entropy] Fix out-of-sync entropy-events state

Changing between "Entropy - Events" results in two dispatches
(`ENTROPY_COUNTS_TOGGLE` and `ENTROPY_DATA`) however the entropy code
would ignore the first update if it didn't contain new entropy data.
This bug has probably existed for the life of the entropy panel however
was masked by those two actions happening back-to-back and being
(always?) bundled together by redux.

Recent work in #1879 (v2.60.0) meant these actions were no longer
back-to-back and thus the bug was revealed.

Closes #1905

src/components/entropy/entropyD3.js

@@ -64,8 +64,9 @@ EntropyChart.prototype.update = function update({
     this._setZoomBounds();
   }
 
+  if (showCounts!==undefined) this.showCounts = showCounts;
+
   if (newBars || selectedPositions!==undefined) {
-    if (showCounts!==undefined) this.showCounts = showCounts;
     if (newBars) {
       this.bars = newBars[0];
       this._updateOffsets();
@@ -75,6 +76,8 @@ EntropyChart.prototype.update = function update({
     if (selectedPositions !== undefined) {
       this.selectedPositions = selectedPositions;
     }
+    /* TODO XXX: there's a potential bug here if selectedCds is set but we don't enter this code block
+    due to the (newBars || selectedPositions!==undefined) conditional */
     if (selectedCds || selectedPositions !== undefined) {
       this._setZoomCoordinates(zoomMin, zoomMax, !!selectedCds);
     }