Connection limit: don't do anything if the limit is not configured

In rabbit_reader:is_over_connection_limit/2.

References #7753, #7787, #7593.

(cherry picked from commit e56e26c)

Author: michaelklishin

deps/rabbit/src/rabbit_reader.erl

@@ -1321,16 +1321,21 @@ is_vhost_alive(VHostPath, User) ->
     end.
 
 is_over_node_connection_limit(Addr, Port) ->
-    Ref = rabbit_networking:ranch_ref(Addr, Port),
-    #{active_connections := ActiveConns} = ranch:info(Ref),
     Limit = rabbit_misc:get_env(rabbit, connection_max, infinity),
-    case ActiveConns > Limit of
-        false -> ok;
-        true ->
-            rabbit_misc:protocol_error(not_allowed,
-                                       "connection refused: "
-                                       "node connection limit (~tp) is reached",
-                                       [Limit])
+    case Limit of
+        infinity -> ok;
+        N when is_integer(N) ->
+            Ref = rabbit_networking:ranch_ref(Addr, Port),
+            #{active_connections := ActiveConns} = ranch:info(Ref),
+
+            case ActiveConns > Limit of
+                false -> ok;
+                true ->
+                    rabbit_misc:protocol_error(not_allowed,
+                                            "connection refused: "
+                                            "node connection limit (~tp) is reached",
+                                            [Limit])
+            end
     end.
 
 is_over_vhost_connection_limit(VHostPath, User) ->