Bug 33177567 The fragment manager is being accessed after it has been torn down. This protects BackStackRecord from accessing the null mHost in that case. Test: cts-tradefed run singleCommand cts -d --skip-preconditions --skip-connectivity-check -m CtsFragmentTestCases Change-Id: Id927eb1bc78e3750b01f685523418bde5a9cf8a0