Prevent autoPlay from playing an animation before it is attached to a window

Fixes #762
diff --git a/lottie/src/main/java/com/airbnb/lottie/LottieAnimationView.java b/lottie/src/main/java/com/airbnb/lottie/LottieAnimationView.java
index c700486..70818b8 100644
--- a/lottie/src/main/java/com/airbnb/lottie/LottieAnimationView.java
+++ b/lottie/src/main/java/com/airbnb/lottie/LottieAnimationView.java
@@ -136,7 +136,7 @@
       }
     }
     if (ta.getBoolean(R.styleable.LottieAnimationView_lottie_autoPlay, false)) {
-      lottieDrawable.playAnimation();
+      wasAnimatingWhenDetached = true;
       autoPlay = true;
     }