[#4367] Fix segfault when unloading account map

sflphone-common/src/managerimpl.cpp

@@ -3900,8 +3900,11 @@ void ManagerImpl::unloadAccountMap ()
 
         _debug ("Manager: Unloading account %s", iter->first.c_str());
 
+        // Avoid removing the IP2IP account twice
+        if(iter->first != "") {
         	delete iter->second;
         	iter->second = NULL;
+        }
 
         iter++;
     }