emacsclient and sublimity cause error

I wrongly reported that upstream:

https://debbugs.gnu.org/cgi/bugreport.cgi?bug=65877

(See therein for a way to reproduce bug.)

The code `(line-number-at-pos (window-start))` appears a couple times in Sublimity, and it should be changed, throughout, to be encapsulated in `(with-current-buffer (window-buffer) …)`.