This is a workaround for a freeze when suspending Helix with C-z on non-Windows systems. The check for the keyboard enhancement protocol locks up crossterm's internal event reading/polling system by trying to set up multiple concurrent readers. `input_stream.next()` sets up one reader looking for regular crossterm events while the `supports_keyboard_enhancement` query sets up another looking for internal events. The latter hangs for two seconds or until the former yields an event. By handling signals first we don't lock up the mutex by trying to read keyboard events.