Misrendering of git 2.24 log --graph

Greetings.

I have observed git 2.24 outputting a garbage graph element for a particular history. The issue does not appear in 2.25, but the underlying bug may still be in there; it is just that _this particular history_ does not expose it anymore due to the new, more compact tree rendering that 2.25 seems to be shipping.

Reproducer:

$ git clone git://github.com/jengelh/git-issue-20200123 gi
$ cd gi; git log --oneline --graph --all --topo-order | head -n 74
[...]
| | * |   ba85ad93c Merge branch 'kc-8.7.x'
| | |\ \  
| |/ / /  
| | | _   
| | * 79106b731 doc: update 8.7.x news

See that underscore there in line 73. The connection between commit 610d621dd and its parent 79106b731 is not properly connected (visually). I think this should have been [diff notation follows]

-| | | _   
+| | | /
+| | |/
 | | * 79106b731 doc: update 8.7.x news

or something along those lines (pun intended).