RecyclerView prefetch: dont change mStructureChanged flag

Some LayoutManager(e.g. leanback) is sensitive to mStructureChanged
flag. Though LinearLayoutManager never uses the flag. The reset to
false flag will cause next onLayoutChildren() of leanback LayoutManager
crash.

Bug: 36595030
Test: RecyclerViewCacheTest.nestedPrefetchNotClearInnerStructureChangeFlag
also did manual check with recompiled TVLauncher.

Change-Id: Ia46fe4fd7ccd9fa3b9ce9c30ff98a62158d5817c
2 files changed