Don't shorten selector string for visual-line-mode and bolp

* avy.el (avy--overlay-at-full): When at an empty line, there's plenty
  of space to display the full selector. No need to truncate it to avoid
  visual-line-mode reformatting the buffer text.

Fixes #129

avy.el

@@ -771,7 +771,8 @@ LEAF is normally ((BEG . END) . WND)."
                                 len))
                            lep)))
           (when (and (bound-and-true-p visual-line-mode)
-                     (> len (- end beg)))
+                     (> len (- end beg))
+                     (not (eq lep beg)))
             (setq len (- end beg))
             (let ((old-str (apply #'string (reverse path))))
               (setq str