Editor crashes when trying to focus a muted subsequence

It appears the hierarchy is invalid for muted sequences, so there is no context to focus them in. 

1. Create a new level sequence
2. Add a subsequence track to the sequence
3. Add two subsequence sections to the track
4. Mute the parent subsequence track
5. Double click one of the subsequences to focus it

RESULT

The editor crashes

UMovieSceneCompiledDataManager::GetHierarchyChecked(FMovieSceneCompiledDataID) MovieSceneCompiledDataManager.h:275
FSequencer::FocusSequenceInstance(UMovieSceneSubSection &) Sequencer.cpp:1159
TSubSectionMixin::OnSectionDoubleClicked(const FGeometry &, const FPointerEvent &) SubTrackEditorBase.h:329
UE::Sequencer::SSequencerSection::OnMouseButtonDoubleClick(const FGeometry &, const FPointerEvent &) SSequencerSection.cpp:1970
`FSlateApplication::RoutePointerDoubleClickEvent'::`2'::<lambda_1>::operator()(const FArrangedWidget &,const FPointerEvent &) SlateApplication.cpp:5770
FEventRouter::Route<FReply,FEventRouter::FBubblePolicy,FPointerEvent,`FSlateApplication::RoutePointerDoubleClickEvent'::`2'::<lambda_1> >(FSlateApplication *,FBubblePolicy,FPointerEvent,const <lambda_1> &,ESlateDebuggingInputEvent) SlateApplication.cpp:442
FSlateApplication::RoutePointerDoubleClickEvent(const FWidgetPath &, const FPointerEvent &) SlateApplication.cpp:5768
FSlateApplication::ProcessMouseButtonDoubleClickEvent(const TSharedPtr<…> &, const FPointerEvent &) SlateApplication.cpp:5751
FSlateApplication::OnMouseDoubleClick(const TSharedPtr<…> &, Type, TVector2<…>) SlateApplication.cpp:5716
FWindowsApplication::ProcessDeferredMessage(const FDeferredWindowsMessage &) WindowsApplication.cpp:2247
FWindowsApplication::DeferMessage(TSharedPtr<…> &, HWND__ *, unsigned int, unsigned long long, long long, int, int, unsigned int) WindowsApplication.cpp:2750
FWindowsApplication::ProcessMessage(HWND__ *, unsigned int, unsigned long long, long long) WindowsApplication.cpp:1097
WindowsApplication_WndProc(HWND__ *, unsigned int, unsigned long long, long long) WindowsApplication.cpp:923
FWindowsApplication::AppWndProc(HWND__ *, unsigned int, unsigned long long, long long) WindowsApplication.cpp:928
<unknown> 0x00007ffc4502ef75
<unknown> 0x00007ffc4502e69d
WinPumpMessages() WindowsPlatformApplicationMisc.cpp:116
FWindowsPlatformApplicationMisc::PumpMessages(bool) WindowsPlatformApplicationMisc.cpp:145
FEngineLoop::Tick() LaunchEngineLoop.cpp:5826
EngineTick() Launch.cpp:61
GuardedMain(const wchar_t *) Launch.cpp:182
LaunchWindowsStartup(HINSTANCE__ *, HINSTANCE__ *, char *, int, const wchar_t *) LaunchWindows.cpp:247
WinMain(HINSTANCE__ *, HINSTANCE__ *, char *, int) LaunchWindows.cpp:298
[Inlined] invoke_main() 0x00007ff76f3edcaa
__scrt_common_main_seh() 0x00007ff76f3edc89
<unknown> 0x00007ffc46447344
<unknown> 0x00007ffc46de26b1