Creation working canvas only if needed.

If images with right size  there is no need in additional working canvas.
Added Logger.Warn, silent return took some time for investigation.

This change makes possible to use CubeTexture in a worker environment in case if images don`t need resizing.

src/Engines/Extensions/engine.cubeTexture.ts

@@ -291,14 +291,6 @@ ThinEngine.prototype.createCubeTexture = function(rootUrl: string, scene: Nullab
             var width = this.needPOTTextures ? ThinEngine.GetExponentOfTwo(imgs[0].width, this._caps.maxCubemapTextureSize) : imgs[0].width;
             var height = width;
 
-            this._prepareWorkingCanvas();
-
-            if (!this._workingCanvas || !this._workingContext) {
-                return;
-            }
-            this._workingCanvas.width = width;
-            this._workingCanvas.height = height;
-
             var faces = [
                 gl.TEXTURE_CUBE_MAP_POSITIVE_X, gl.TEXTURE_CUBE_MAP_POSITIVE_Y, gl.TEXTURE_CUBE_MAP_POSITIVE_Z,
                 gl.TEXTURE_CUBE_MAP_NEGATIVE_X, gl.TEXTURE_CUBE_MAP_NEGATIVE_Y, gl.TEXTURE_CUBE_MAP_NEGATIVE_Z
@@ -310,6 +302,16 @@ ThinEngine.prototype.createCubeTexture = function(rootUrl: string, scene: Nullab
             let internalFormat = format ? this._getInternalFormat(format) : this._gl.RGBA;
             for (var index = 0; index < faces.length; index++) {
                 if (imgs[index].width !== width || imgs[index].height !== height) {
+                    
+                    this._prepareWorkingCanvas();
+
+                    if (!this._workingCanvas || !this._workingContext) {
+                        Logger.Warn("Cannot create canvas to resize texture.");
+                        return;
+                    }
+                    this._workingCanvas.width = width;
+                    this._workingCanvas.height = height;
+                    
                     this._workingContext.drawImage(imgs[index], 0, 0, imgs[index].width, imgs[index].height, 0, 0, width, height);
                     gl.texImage2D(faces[index], 0, internalFormat, internalFormat, gl.UNSIGNED_BYTE, this._workingCanvas);
                 } else {
@@ -342,4 +344,4 @@ ThinEngine.prototype.createCubeTexture = function(rootUrl: string, scene: Nullab
     this._internalTexturesCache.push(texture);
 
     return texture;
-};
+};