Visual Studio 2019 (16.4.5) Compiler Warning

I am getting a warning when compiling:

`libstdaudio\include\audio_backend\__wasapi_backend.h(172): warning C4715: 'std::experimental::audio_device::operator=': not all control paths return a value`

It seems `audio_device& operator=(audio_device&& other) noexcept` is missing a `return *this`.
