unified palette: don't animate scrolling if delta is zero

HISTORY.md

@@ -22,6 +22,8 @@
 * gui: unified palette: indicate "selected" category in selector buttons
 * extensions: web-serial extension primitives, pioneered by Dariusz Dorożalski
 * added new "serial ports" library
+* added jshint esversion tags
+* gui: unified palette: don't animate scrolling if delta is zero
 
 ### 2021-07-04
 * fixed audio_comp library "plot sound" block to work with translations, thanks, Hans, for the report!

src/gui.js

@@ -2569,6 +2569,7 @@ IDE_Morph.prototype.scrollPaletteToCategory = function (category) {
     );
     if (firstInCategory === undefined) {return; }
     delta = palette.top() - firstInCategory.top() + palette.padding;
+    if (delta === 0) {return; }
     this.world().animations.push(new Animation(
         y => { // setter
             palette.contents.setTop(y);