Prevent a crash on older versions of Android (#1148)

Fixes #1143
diff --git a/lottie/src/main/java/com/airbnb/lottie/LottieAnimationView.java b/lottie/src/main/java/com/airbnb/lottie/LottieAnimationView.java
index 3ca0233..9f125e8 100644
--- a/lottie/src/main/java/com/airbnb/lottie/LottieAnimationView.java
+++ b/lottie/src/main/java/com/airbnb/lottie/LottieAnimationView.java
@@ -232,6 +232,12 @@
 
   @Override
   protected void onVisibilityChanged(@NonNull View changedView, int visibility) {
+    // This can happen on older versions of Android because onVisibilityChanged gets called from the
+    // constructor of View so this will get called before lottieDrawable gets initialized.
+    // https://github.com/airbnb/lottie-android/issues/1143
+    if (lottieDrawable == null) {
+      return;
+    }
     if (visibility == VISIBLE) {
       if (wasAnimatingWhenVisibilityChanged) {
         resumeAnimation();