patch 9.2.0796: Visual block reselection wrong with 'virtualedit'

patch 9.2.0796: Visual block reselection wrong with 'virtualedit'

Problem:  Visual block reselection wrong with 'virtualedit' when line
          lengths are different (Alex Yang, after 8.2.3494).
Solution: Set the entire cursor position to old position when computing
          target curswant, since the check_cursor() added in 8.2.3494
          may change cursor column as well (zeertzjq).

fixes:  #20746
closes: #20748

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>