Fix crash when a list updates while a screen reader reads an item

[mehranlatifi83]

Summary

With a screen reader running, the app crashes from time to time when a list updates underneath it, most reliably when messages load into an empty chat that was opened from search, from a global search result or from a comment thread, and when scrolling to the end of comments loads more.

java.lang.IndexOutOfBoundsException: invalid position 61. State item count is 24
  at RecyclerView$Recycler.convertPreLayoutPositionToPostLayout
  at GridLayoutManager.getSpanGroupIndex
  at GridLayoutManager.onInitializeAccessibilityNodeInfoForItem
  at RecyclerViewAccessibilityDelegate$ItemDelegate.onInitializeAccessibilityNodeInfo
  at ChatMessageCell.onInitializeAccessibilityNodeInfo
  at ViewRootImpl.handleWindowContentChangedEvent
  ...
  at RecyclerView.dispatchContentChangedIfNecessary
  at RecyclerView.onExitLayoutOrScroll
  at RecyclerView.dispatchLayoutStep1

The list dispatches a content changed event from inside its layout pass. Because a screen reader holds accessibility focus on an item, the framework builds that item's node info right away, which asks the layout manager for the item position while the ongoing layout has not settled positions yet, and the stale position is out of range for the new state. Without a screen reader the node is never built, which is why it only happens with one running.

The delegate already ignores the layout manager while adapter updates are pending. This extends the same guard to a running layout pass. The node is filled again once the layout is over, so nothing is lost for the screen reader.

[amirmahdifard]

@oldeepsmile-beep hi. Can this be merged? we always had problems why no one pays any attention to pull requests opened here. About accessibility, no one pays any attention to us, So we just started to send the pull requests our selves.