patch 9.1.0708: Recursive window update does not account for reset skipcol

patch 9.1.0708: Recursive window update does not account for reset skipcol

Problem:  Window is updated with potentially invalid skipcol in recursive
          window update path. I.e. cursor outside of visible range in
          large line that does not fit.
Solution: Make sure it is valid (Luuk van Baal).

closes: #15605

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