patch 9.1.0488: Wrong padding for pum "kind" with 'rightleft'

patch 9.1.0488: Wrong padding for pum "kind" with 'rightleft'

Problem:  Wrong padding for pum "kind" with 'rightleft'.
Solution: Fix off-by-one error (zeertzjq).

The screen_fill() above is end-exclusive, and
- With 'rightleft' it fills `pum_col - pum_base_width - n + 1` to `col`,
  so the next `col` should be `pum_col - pum_base_width - n`.
- With 'norightleft' it fills `col` to `pum_col - pum_base_width + n - 1`,
  so the next `col` should be `pum_col - pum_base_width + n`.

closes: #15004

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