server: Protect several fields from potentially pointing to bad memory

Source/cmConnection.cxx

@@ -118,7 +118,9 @@ void cmEventBasedConnection::OnDisconnect(int onerror)
 {
   (void)onerror;
   this->OnConnectionShuttingDown();
-  this->Server->OnDisconnect(this);
+  if (this->Server) {
+    this->Server->OnDisconnect(this);
+  }
 }
 
 cmConnection::~cmConnection()
@@ -127,6 +129,7 @@ cmConnection::~cmConnection()
 
 bool cmConnection::OnConnectionShuttingDown()
 {
+  this->Server = nullptr;
   return true;
 }
 

Source/cmServerConnection.cxx

@@ -53,6 +53,9 @@ void cmStdIoConnection::SetupStream(uv_stream_t*& stream, int file_id)
 void cmStdIoConnection::SetServer(cmServerBase* s)
 {
   cmConnection::SetServer(s);
+  if (!s) {
+    return;
+  }
 
   SetupStream(this->ReadStream, 0);
   SetupStream(this->WriteStream, 1);