onDrawScrollIndicators returns early if the view isn't attached

Test: Install a test app that can reproduce the null pointer
      exception. Flash and install a build with this CL. Null
      pointer exception can no longer be observed.

Bug: 183386115
Change-Id: Iab155dfca20e0119cc401d111ace23e416e93b93

core/java/android/view/View.java

@@ -19782,6 +19782,11 @@ public class View implements Drawable.Callback, KeyEvent.Callback,
             return;
         }
 
+        if (mAttachInfo == null) {
+            // View is not attached.
+            return;
+        }
+
         final int h = dr.getIntrinsicHeight();
         final int w = dr.getIntrinsicWidth();
         final Rect rect = mAttachInfo.mTmpInvalRect;