Fixed SHUTDOWN message with a wrong (uninitialized) DST socket ID

[maxsharabayko]

CUDT::m_PeerID is not initialized by the constructor. It has a random (garbage) value until set during HS.

When a caller with a passphrase tries to connect to a listener without a passphrase, the listener sends a rejection conclusion HS.
The caller, receiving the HS, sees the rejection code (in CUDT::processAsyncConnectRequest(..)), and returns from the function without initializing m_PeerID.
As processAsyncConnectRequest(..) returns false, a SHUTDOWN control packet is sent from CRendezvousQueue::updateConnStatus(..).
But destination SRT socket ID is still not initialized and may contain some garbage value, that could match some existing SRT socket ID on the listener side.
In the worst case, it could lead to a closure of a different valid connection existing on the same port, when SHUTDOWN is sent from the same IP.