Crash Occurs Enabling new Audio Mixer with Audio Devices Disabled

If a user has all their audio devices disabled, and then enables the new audio mixer for 4.16, a crash occurs when trying to launch any new or existing project.

This is a regression as this crash does not occur in the 4.15.3 engine version.

1. Disable all audio devices on machine.
2. Enable new Audio Mixer.
3. Create new 4.16 project.

Outcome Crash occurs.

Expected Does not crash and continues to load editor despite all audio devices being disabled.

UE4Editor_AudioMixerXAudio2!Audio::FMixerPlatformXAudio2::StopAudioStream() audiomixerplatformxaudio2.cpp:407
UE4Editor_AudioMixer!Audio::FMixerDevice::TeardownHardware() audiomixerdevice.cpp:206
UE4Editor_Engine!FAudioDevice::Teardown() audiodevice.cpp:380
UE4Editor_Engine!FAudioDevice::Init() audiodevice.cpp:284
UE4Editor_Engine!FAudioDeviceManager::CreateAudioDevice() audiodevicemanager.cpp:147
UE4Editor_Engine!UEngine::InitializeAudioDeviceManager() unrealengine.cpp:2056
UE4Editor_Engine!UEngine::Init() unrealengine.cpp:958
UE4Editor_UnrealEd!UEditorEngine::InitEditor() editorengine.cpp:559
UE4Editor_UnrealEd!UEditorEngine::Init() editorengine.cpp:847
UE4Editor_UnrealEd!UUnrealEdEngine::Init() unrealedengine.cpp:75
UE4Editor!FEngineLoop::Init() launchengineloop.cpp:2588
UE4Editor_UnrealEd!EditorInit() unrealedglobals.cpp:76
UE4Editor!GuardedMain() launch.cpp:150
UE4Editor!GuardedMainWrapper() launchwindows.cpp:134
UE4Editor!WinMain() launchwindows.cpp:210
UE4Editor!__scrt_common_main_seh() exe_common.inl:264
kernel32!BaseThreadInitThunk()
ntdll!RtlUserThreadStart()