Bug 1302424 - Check panelStateChangeListener isn't null before using it. r=Grisha

MozReview-Commit-ID: GogUQ4edJvU

--HG--
extra : rebase_source : 9b5072ab2b5b8eea5af4023e3f8de79cafe4b8b5

mobile/android/base/java/org/mozilla/gecko/home/CombinedHistoryAdapter.java

@@ -154,7 +154,7 @@ public class CombinedHistoryAdapter extends RecyclerView.Adapter<CombinedHistory
                             notifyItemRemoved(RECENT_TABS_SMARTFOLDER_INDEX);
                         }
 
-                        if (countReliable) {
+                        if (countReliable && panelStateChangeListener != null) {
                             panelStateChangeListener.setCachedRecentTabsCount(recentTabsCount);
                         }
                     }