bug#52446: 28.0.90; Infinite loop in add_row_entry

[Po Lu]

Emacs froze while I was scrolling through a large image with `C-n'.  The
source of the freeze was an infinite loop in this part of
`add_row_entry':

    while (entry && !row_equal_p (entry->row, row, 1))
--->  entry = entry->next;

The problem seems to be that `entry' points to the same address as
`entry->next'.