[BUG] gitk: clicking on a connecting line produces can't read "cflist_top"

Clicking on a line that connects commit nodes produces this error:

can't read "cflist_top": no such variable
can't read "cflist_top": no such variable
    while executing
"$cflist tag remove highlight $cflist_top.0 "$cflist_top.0 lineend""
    (procedure "highlightfile" line 4)
    invoked from within
"highlightfile 0"
    (procedure "highlightfile_for_scrollpos" line 8)
    invoked from within
"highlightfile_for_scrollpos $topidx"
    (procedure "scrolltext" line 9)
    invoked from within
"scrolltext 0.0 1.0"
    (vertical scrolling command executed by text)

Bisection points to b967135d (Synchronize highlighting in file view when scrolling diff).

gitk remains responsive after the error window is closed, so it is not urgent. A fix would be appreciated nevertheless.

-- Hannes