fixed flickering issue with maps module

src/maps.js

@@ -38,7 +38,7 @@
 
 // Global stuff ////////////////////////////////////////////////////////
 
-modules.maps = '2020-March-19';
+modules.maps = '2020-March-25';
 
 // WorldMap /////////////////////////////////////////////////////////////
 
@@ -287,7 +287,10 @@ WorldMap.prototype.render = function () {
         }
     }
 
-    this.canvas = newCanvas(this.extent, true, this.canvas);
+    // create a new canvas. Note, we cannot reuse the existing canvas,
+    // because it could be queried while tiles are still rendering
+    this.canvas = newCanvas(this.extent, true);
+
     ctx = this.canvas.getContext('2d');
     for (x = 0; x < tileGrid.x; x += 1) {
         for (y = 0; y < tileGrid.y; y += 1) {

src/objects.js

@@ -3484,6 +3484,7 @@ SpriteMorph.prototype.wearCostume = function (costume, noShadow) {
         y = this.yPosition ? this.yPosition() : null,
         idx = isNil(costume) ? null : this.costumes.asArray().indexOf(costume),
         isWarped = this.isWarped;
+
     if (isWarped) {
         this.endWarp();
     }