Martino Ferrari
dc0a977c86
Zeroing an unusable wheel amount turned it into a zero-notch zoom: the factor was exactly one, the range did not change, but the zoom body still ran through set_x_range/set_y_range, which clear auto_scale unconditionally. One garbage wheel therefore disarmed auto-fit on every axis. on_wheel now rejects an unusable amount before the event can mutate anything, keeping the position fallback. The tests that should have caught it are strengthened: the wheel case now asserts auto scale is still armed (it was passing either way), and the invalid-position case checks a pan measured from the last real position with the drag alive, rather than a range nothing could have moved.