patch 9.2.0413: Scrolling wrong with 'splitkeep' when changing 'cmdheight'

patch 9.2.0413: Scrolling wrong with 'splitkeep' when changing 'cmdheight'

Problem:  Cursor is not adjusted when 'cmdheight' is changed to cover
          the cursor with 'splitkeep' ~= "cursor".
Solution: Handle window resize for 'splitkeep' after changing 'cmdheight'.
          Ensure previous window height is set when changing 'splitkeep'
          (Luuk van Baal).

closes: #20043

Signed-off-by: Luuk van Baal <luukvbaal@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>