patch 9.1.0956: completion may crash, completion highlight wrong with preview window

patch 9.1.0956: completion may crash, completion highlight wrong with preview window

Problem:  completion may crash, completion highlight wrong with preview
          window (after v9.1.0954)
Solution: correctly calculate scroll offset, check for preview window
          when adding extra highlighting
          (glepnir)

when there have a preview window prepare_tagpreview
will change curwin to preview window and this may cause
ComplMatchIns check condition not correct. check wp is curwin
and also the type of wp is not a preview or poup info

fixes: #16284
closes: #16283

Signed-off-by: glepnir <glephunter@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>