Added a single source of SDL object IDs

This ensures that we don't accidentally interpret an ID from one system as an ID in another system.
Audio device IDs are not covered here, since they have a unique numbering system.

src/joystick/virtual/SDL_virtualjoystick.c

@@ -237,7 +237,7 @@ SDL_JoystickID SDL_JoystickAttachVirtualInner(const SDL_VirtualJoystickDesc *des
     }
 
     /* Allocate an instance ID for this device */
-    hwdata->instance_id = SDL_GetNextJoystickInstanceID();
+    hwdata->instance_id = SDL_GetNextObjectID();
 
     /* Add virtual joystick to SDL-global lists */
     if (g_VJoys) {