with-editor-locate-emacsclient: don't assume version string length

Emacs usually identifies itself as "N.M.1" or "N.0.[59][0-9]"
but at least one users Emacs identifies itself as just "N.M",
so stop assuming that the version string always consist of at
least three elements.

Fixes #33.

with-editor.el

@@ -106,7 +106,9 @@
 
 (defun with-editor-locate-emacsclient ()
   "Search for a suitable Emacsclient executable."
-  (or (with-editor-locate-emacsclient-1 (with-editor-emacsclient-path) 3)
+  (or (with-editor-locate-emacsclient-1
+       (with-editor-emacsclient-path)
+       (length (split-string emacs-version "\\.")))
       (prog1 nil (display-warning 'with-editor "\
 Cannot determine a suitable Emacsclient