dinput: Add error check to silence a compiler warning.

dlls/dinput/config.c

@@ -298,10 +298,11 @@ static void assign_action(HWND dialog)
     int obj = lv_get_cur_item(dialog);
     int old_action = lv_get_item_data(dialog, obj);
     int used_obj;
-
-    DIDEVICEOBJECTINSTANCEW ddo = device->ddo[obj];
+    DWORD type;
 
     if (old_action == action) return;
+    if (obj < 0) return;
+    type = device->ddo[obj].dwType;
 
     /* Clear old action */
     if (old_action != -1)
@@ -320,7 +321,7 @@ static void assign_action(HWND dialog)
     lv_set_action(dialog, used_obj, -1, lpdiaf);
 
     /* Set new action */
-    lpdiaf->rgoAction[action].dwObjID = ddo.dwType;
+    lpdiaf->rgoAction[action].dwObjID = type;
     lpdiaf->rgoAction[action].guidInstance = device->ddi.guidInstance;
     lpdiaf->rgoAction[action].dwHow = DIAH_USERCONFIG;