fix: check window when restore scrolloff

[phanen]

Reproduce by:

:set scrolloff=10
:tabnew | copen | tabclose

Error executing vim.schedule lua callback: [string ":lua"]:1: Invalid window id: 1009
stack traceback:
        [C]: in function '__newindex'
        [string ":lua"]:1: in function <[string ":lua"]:1>