Since the wxWidgets 3.3 upgrade the Slice/Print split-button's transient
popup was dismissed the moment the cursor entered the gap between the
button and the menu, making "Print -> Export" impossible to select.
Anchor the menu flush against the button (with a 2 px overlap) instead of
6 px below it, removing the dead-zone the cursor had to cross.
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
