[cpp-tests] SpritePolygonTest invoke UISlide::setPercent after initialization (cocos2d#19676)

* delay onProgressChange event when setProgress

* Revert "delay onProgressChange event when setProgress"

This reverts commit a9ad090.

* setPercent after initialization

Author: PatriceJiang

tests/cpp-tests/Classes/SpritePolygonTest/SpritePolygonTest.cpp

@@ -294,15 +294,16 @@ void SpritePolygonTestSlider::initSliders()
     slider->loadSlidBallTextures("cocosui/sliderThumb.png", "cocosui/sliderThumb.png", "");
     slider->loadProgressBarTexture("cocosui/sliderProgress.png");
     slider->setPosition(Vec2(vsize.width/2, vsize.height/4));
-    
-    slider->addEventListener(CC_CALLBACK_2(SpritePolygonTestSlider::changeEpsilon, this));
-    slider->setPercent((int)(sqrtf(1.0f/19.0f)*100));
-    
+
     auto ttfConfig = TTFConfig("fonts/arial.ttf", 8);
     _epsilonLabel = Label::createWithTTF(ttfConfig, "Epsilon: 2.0");
     addChild(_epsilonLabel);
     _epsilonLabel->setPosition(Vec2(vsize.width/2, vsize.height/4 + 15));
     addChild(slider);
+
+    slider->addEventListener(CC_CALLBACK_2(SpritePolygonTestSlider::changeEpsilon, this));
+    slider->setPercent((int)(sqrtf(1.0f/19.0f)*100));
+
 }
 
 void SpritePolygonTestSlider::makeSprites(const std::string* list, const int count, const float y)