Problem:
Since 5181984d, `nvim_exec_autocmds({buf=…})` temporarily sets the
`buf`-window as current-window, and its statusline renders as
a "current-window statusline", regardless of the user's actual
current-window.
Solution:
Mark the statusline for redraw in `aucmd_restbuf()`, so it is redrawn
correctly after the event.
Co-authored-by: Luuk van Baal <luukvbaal@gmail.com>