VAutoHider: cleanup size_allocate

[danirabbit]

• Avoid nesting and using continue where possible
• Brackets with if statements
• DRY more_label hide and vexpand
• rename height to shown_children_height for clarity

[jeremypw]

This seems to alter the behaviour when there is only one event. The more_label appears when there is less space than the child height + more_label_height whereas in master it appears when there is less space available than the child_height. So the more_label appears earlier than necessary when shrinking the height.

It would simplify matters if we can assume/ensure the child height is constant and the same as the more_label height.

[danirabbit]

@jeremypw ah thanks for noticing that! I think it should be fixed now. The logic here was pretty hard to follow. Hopefully it's a little clearer now

[jeremypw]

Works as expected now, thanks.