segmentation: Reset min_segment on data update
segmentation: Reset min_segment on data update

Without this it is possible to reach an inconsistent
state where min_segment > max_segment if for example:
Rate control drives toward base_q_idx = 1 resulting in
min_segment == max_segment. At the next keyframe,
max_segment decreases as fewer segments are selected
while min_segment is unchanged.

xiph/rav1e,xiph/rav1e