Add null check in stopActionModeOrContextMenu().

Fixes: 33378283

Change-Id: I9ff6f73d8c757f8acc2672b812023b0c683b07c6
diff --git a/src/com/android/calculator2/HistoryFragment.java b/src/com/android/calculator2/HistoryFragment.java
index 6e54d9f..5e93d50 100644
--- a/src/com/android/calculator2/HistoryFragment.java
+++ b/src/com/android/calculator2/HistoryFragment.java
@@ -241,6 +241,9 @@
     }
 
     public boolean stopActionModeOrContextMenu() {
+        if (mRecyclerView == null) {
+            return false;
+        }
         for (int i = 0; i < mRecyclerView.getChildCount(); i++) {
             final View view = mRecyclerView.getChildAt(i);
             final HistoryAdapter.ViewHolder viewHolder =