fix #923: move NetworkManager.OnApplicationQuit Transport Shutdown co…

…de into Transport.OnApplicationQuit. Fixes a potential bug where the Transport wouldn't be shut down if someone doesn't use the NetworkManager.

Assets/Mirror/Runtime/NetworkManager.cs

@@ -642,12 +642,6 @@ public virtual void OnApplicationQuit()
                 StopServer();
                 print("OnApplicationQuit: stopped server");
             }
-
-            // stop transport (e.g. to shut down threads)
-            // (when pressing Stop in the Editor, Unity keeps threads alive
-            //  until we press Start again. so if Transports use threads, we
-            //  really want them to end now and not after next start)
-            Transport.activeTransport.Shutdown();
         }
 
         /// <summary>

Assets/Mirror/Runtime/Transport/Transport.cs

@@ -204,5 +204,18 @@ public virtual bool GetConnectionInfo(int connectionId, out string address)
         //            ShoulderRotation.LateUpdate, resulting in projectile
         //            spawns at the point before shoulder rotation.
         public void Update() { }
+
+        /// <summary>
+        /// called when quitting the application by closing the window / pressing stop in the editor
+        /// <para>virtual so that inheriting classes' OnApplicationQuit() can call base.OnApplicationQuit() too</para>
+        /// </summary>
+        public virtual void OnApplicationQuit()
+        {
+            // stop transport (e.g. to shut down threads)
+            // (when pressing Stop in the Editor, Unity keeps threads alive
+            //  until we press Start again. so if Transports use threads, we
+            //  really want them to end now and not after next start)
+            Shutdown();
+        }
     }
 }