patch 9.1.0896: completion list wrong after v9.1.0891

patch 9.1.0896: completion list wrong after v9.1.0891

Problem:  completion list wrong after v9.1.0891
Solution: update compl_mach_array after leader change
          (glepnir)

compl_shown_match update not correct after refactoring in v9.1.0891
Unfortunately, this regressed what item is selected after leader change.

So generate compl_match_array before updating compl_shown_match range,
and split generate compl_match_array into range match_head

fixes: #16128
closes: #16129

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