Added initial value to mUsingNamedFrame, which caused crashes on copyTo();

engine/source/2d/assets/ParticleAssetEmitter.cc

@@ -205,6 +205,7 @@ ParticleAssetEmitter::ParticleAssetEmitter() :
     mAnimationAsset.registerRefreshNotify( this );
     
     mNamedImageFrame = "";
+    mUsingNamedFrame = false;
 }
 
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