MT#62253 log: AmSession: log only when dlg is added already

Otherwise we can end up with:

Program terminated with signal SIGSEGV, Segmentation fault.
104     ./core/AmSession.cpp: No such file or directory.
[Current thread is 1 (Thread 0x7fc7dd677e40 (LWP 176249))]

Change-Id: Ia61de0caa9b1764839c740e62bc3f463da4ed4dc

core/AmSession.cpp

@@ -88,9 +88,10 @@ AmSession::AmSession(AmSipDialog* p_dlg)
   , _pid(this)
 #endif
 {
-  ILOG_DLG(L_DBG, "dlg = %p",dlg);
   if(!dlg) dlg = new AmSipDialog(this);
   else dlg->setEventhandler(this);
+
+  ILOG_DLG(L_DBG, "dlg = %p",dlg);
 }
 
 AmSession::~AmSession()