patch 9.1.1295: clientserver: does not handle :stopinsert correctly

patch 9.1.1295: clientserver: does not handle :stopinsert correctly

Problem:  clientserver: When in insert mode, a :stopinsert command
          is not correctly processed (user202729)
Solution: If the :stopinsert command is received while waiting for
          input, stuff the NOP key into the type-ahead buffer and
          detect that :stopinsert was used in edit() so that the
          cursor position is decremented.

fixes: #17016
closes: #17024

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