[C++] Archive Client AsyncConnect::poll: Avoid proceeding to step 1 until m_subscription is non-null (#1196)
[C++] Archive Client AsyncConnect::poll: Avoid proceeding to step 1 until m_subscription is non-null (#1196)

* Avoid proceeding to step 1 until m_subscription is non-null

findSubscription() may return a null pointer that is used unchecked in step 1,

* Avoid null pointer access in timeout message
mikeb01/Aeron,mikeb01/Aeron,mikeb01/Aeron,mikeb01/Aeron