server: Z21 ClientKernel fix crash on disconnect

See traintastic#53
When disabling communications, kernel object is deleted
but EventLoop callback will run after and access deleted
object through captured 'this'
Temporary fix for this problem is to copy log ID value instead.

server/src/hardware/protocol/z21/clientkernel.cpp

@@ -53,9 +53,9 @@ void ClientKernel::receive(const Message& message)
 {
   if(m_config.debugLogRXTX)
     EventLoop::call(
-      [this, msg=toString(message)]()
+      [logId=m_logId, msg=toString(message)]()
       {
-        Log::log(m_logId, LogMessage::D2002_RX_X, msg);
+        Log::log(logId, LogMessage::D2002_RX_X, msg);
       });
 
   switch(message.header())