When insertBlanks clears the entire region from cursor to the right margin (scroll_amount == 0), a wide character whose head is at the right margin gets cleared but its spacer_tail just beyond the margin is left behind, causing a "spacer tail not following wide" page integrity violation. Move the right-margin wide-char cleanup from inside the scroll_amount > 0 block to before it, so it runs unconditionally — matching the rowWillBeShifted pattern of cleaning up boundary-straddling wide chars up front. Found via AFL++ fuzzing. #11109