asyncio: Fix _format_coroutine for coroutine-like objects w/o __name__

asyncio: Fix _format_coroutine for coroutine-like objects w/o __name__

Some built-in coroutine-like objects might not have __name__ or
__qualname__. A good example of such are 'asend', 'aclose' and
'athrow' coroutine methods of asynchronous generators.