Set message identifier to null pointer in the Message paremt class as it should be set by child class. Better core early,.. Actually this fixes a strange segfault in the server version when adding the first channel

sdrbase/util/message.cpp

@@ -20,7 +20,7 @@
 #include "util/message.h"
 #include "util/messagequeue.h"
 
-const char* Message::m_identifier = "Message";
+const char* Message::m_identifier = 0;
 
 Message::Message() :
 	m_destination(0)