windows default executor is not exception safe.

[feverzsj]

Newly allocated f is not guarded against later throw.

libraries/stlab/concurrency/default_executor.hpp

Lines 164 to 169 in c59cfac

	auto work = CreateThreadpoolWork(&callback_impl<F>, new F(std::forward<F>(f)),
	&_callBackEnvironment);
	if (work == nullptr) {
	throw std::bad_alloc();
	}