Don't set PN until message router has been instantiated

sbapp/sideband/core.py

@@ -151,6 +151,7 @@ class SidebandCore():
         self.default_lxm_limit = 128*1000
         self.state_db = {}
         self.state_lock = Lock()
+        self.message_router = None
         self.rpc_connection = None
         self.service_stopped = False
         self.service_context = service_context
@@ -859,6 +860,7 @@ class SidebandCore():
             RNS.log("No active propagation node configured")
         else:
             try:
+                if self.message_router:
                     self.active_propagation_node = dest
                     self.config["last_lxmf_propagation_node"] = dest
                     self.message_router.set_outbound_propagation_node(dest)