bug#27879: Bad behavior with sr-speedbar package

[Angelo Graziosi <angelo.graziosi@alice.it>]

With recent builds from master, after 20170728 - 
f1ed31a8f5c6f19aa5e119e670533241c6375945 commit, visiting a buffer 
produces a "New window below" (C-x 2) and the buffer shows up in the 
bottom window.

Usually, when one visits a buffer this is in the current window without 
splitting..

I can reproduce this behavior on GNU/Linux Mint 18.2 x64 (Mate), W64 
(MSYS2/MINGW64) and macOS Sierra (10.12.6, NS build). This is the 
minimal ~/.emacs.d/init.el:

$ cat init.el
;; Adds the MELPA repo to Emacs Packages
(when (>= emacs-major-version 24)
   (require 'package)
   (add-to-list
    'package-archives
    '("melpa" . "http://melpa.org/packages/")
    t)
   (package-initialize))

(require 'sr-speedbar)

Steps:

1. Start Emacs. It starts with a single window containing the *GNU 
Emacs* buffer.

2. Now toggle the sr-speedbar: M-x sr-speedbar-toggle. It contains two 
windows: on the right, the sr-speedbar; on the left the *GNU Emacs* buffer.

3. In *GNU Emacs* buffer visit a buffer: C-x C-f foo.txt. The *GNU 
Emacs* buffer window is divided (as in C-x 2) and foo.txt is in the 
bottom window.

The last master with the right behavior is 2017-07-28 12:38:22 +0300, 
f1ed31a8f5c6f19aa5e119e670533241c6375945.


Ciao,
   Angelo.