Simplify code and cover all cases correctly CesiumGS#5819

Author: Josh Bernstein

Source/DataSources/KmlDataSource.js

@@ -729,6 +729,12 @@ define([
 
         var iconNode = queryFirstNode(node, 'Icon', namespaces.kml);
         var icon = getIconHref(iconNode, dataSource, sourceUri, uriResolver, false, query);
+
+        // If icon tags are present but blank, we do not want to show an icon
+        if (defined(iconNode) && !defined(icon)) {
+            icon = false;
+        }
+
         var x = queryNumericValue(iconNode, 'x', namespaces.gx);
         var y = queryNumericValue(iconNode, 'y', namespaces.gx);
         var w = queryNumericValue(iconNode, 'w', namespaces.gx);
@@ -1138,8 +1144,10 @@ define([
             entity.billboard = billboard;
         }
 
-        if (!defined(styleEntity.billboard) && !defined(billboard.image)) {
+        if (!defined(billboard.image)) {
             billboard.image = dataSource._pinBuilder.fromColor(Color.YELLOW, 64);
+        } else if (billboard.image == false) {
+            billboard.image = undefined;
         }
 
         var scale = 1.0;