Crash with Gridlayout

Hi All,

I am getting below crash randomly when we render the leanback fragment

```
java.lang.NullPointerException: Attempt to invoke virtual method 'boolean androidx.recyclerview.widget.RecyclerView$State.isPreLayout()' on a null object reference
08-11 18:11:23.668 E/AndroidRuntime(16942): at androidx.leanback.widget.GridLayoutManager$2.addItem(GridLayoutManager.java:1704)
08-11 18:11:23.668 E/AndroidRuntime(16942): at androidx.leanback.widget.SingleRow.prependVisibleItems(SingleRow.java:93)
08-11 18:11:23.668 E/AndroidRuntime(16942): at androidx.leanback.widget.Grid.prependVisibleItems(Grid.java:371)
08-11 18:11:23.668 E/AndroidRuntime(16942): at androidx.leanback.widget.GridLayoutManager.prependVisibleItems(GridLayoutManager.java:1940)
08-11 18:11:23.668 E/AndroidRuntime(16942): at androidx.leanback.widget.GridLayoutManager.scrollDirectionPrimary(GridLayoutManager.java:2455)
08-11 18:11:23.668 E/AndroidRuntime(16942): at androidx.leanback.widget.GridLayoutManager.scrollVerticallyBy(GridLayoutManager.java:2406)
08-11 18:11:23.668 E/AndroidRuntime(16942): at androidx.recyclerview.widget.RecyclerView.scrollStep(RecyclerView.java:1972)
08-11 18:11:23.668 E/AndroidRuntime(16942): at androidx.recyclerview.widget.RecyclerView$ViewFlinger.run(RecyclerView.java:5476)
08-11 18:11:23.668 E/AndroidRuntime(16942): at android.view.Choreographer$CallbackRecord.run(Choreographer.java:781)
08-11 18:11:23.668 E/AndroidRuntime(16942): at android.view.Choreographer.doCallbacks(Choreographer.java:592)
08-11 18:11:23.668 E/AndroidRuntime(16942): at android.view.Choreographer.doFrame(Choreographer.java:559)
08-11 18:11:23.668 E/AndroidRuntime(16942): at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:767)
08-11 18:11:23.668 E/AndroidRuntime(16942): at android.os.Handler.handleCallback(Handler.java:739)
08-11 18:11:23.668 E/AndroidRuntime(16942): at android.os.Handler.dispatchMessage(Handler.java:95)
08-11 18:11:23.668 E/AndroidRuntime(16942): at android.os.Looper.loop(Looper.java:135)
08-11 18:11:23.668 E/AndroidRuntime(16942): at android.app.ActivityThread.main(ActivityThread.java:5604)
08-11 18:11:23.668 E/AndroidRuntime(16942): at java.lang.reflect.Method.invoke(Native Method)
08-11 18:11:23.668 E/AndroidRuntime(16942): at java.lang.reflect.Method.invoke(Method.java:372)
08-11 18:11:23.668 E/AndroidRuntime(16942): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:984)
08-11 18:11:23.668 E/AndroidRuntime(16942): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:779)
```

How to fix this

Start with the stack trace at GridLayoutManager.java:1704, then trace the call path through SingleRow.java, Grid.java, and the Leanback fragment rendering flow. Reproduce the random crash while rendering or scrolling and establish a reliable trigger; done means the trigger no longer produces the null-state crash and the relevant behavior is covered by a regression check.

Written by the indexing model from the issue text.