Change km_dokey() to pass SigWinch on for the MENU_EDITOR. (see #3877)

Change km_dokey() to pass SigWinch on for the MENU_EDITOR. (see #3877)

Change _mutt_enter_string() to pass the SigWinch through for
_mutt_get_field() or mutt_enter_string() to handle.

Add a call to mutt_current_menu() in _mutt_get_field() to properly
redisplay the screen in that case.