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Describe the bug

indev->group is kept when group is deleted.

When I delete a group (group_del()), that group could still be assigned to an indev (lv_indev_set_group()).
As the objects in the group are 'told' the group is deleted, I would assume the indev is as well. But it is not. I had to make a workaround for this as I'm deleting groups, setting lv_indev_set_group(indev, nullptr) to remove it.
Not sure if this is intended behaviour but since these kind of things seem to be taken care of in the rest of LVGL I would think this is a bug.

To Reproduce

v_group_t* g = lv_group_create();
lv_indev_set_group(g);
lv_group_del(g);
have some fun with your indev->group

Expected behavior

I think group_del shoudl iterate the indev's to see if anyone has its group set to the one going to be deleted.

Screenshots or video