Remove lines with no effect: (unless limit (setf limit nil)) -> if limit...

Remove lines with no effect: (unless limit (setf limit nil)) -> if limit==nil then limit=nil
Rewrite decision conditions to simpler equivalents
Remove (when (= (point-max) (+ (buffer-size) 1))) on the else branch of the if with same condition negated: condition always true (remove unnecessary evaluation of point-max and buffer-size)