bug#17942: 24.3.92; pos-visible-in-window-p with PARTIALLY is wrong for the first row only containing a single image

[YAMAMOTO Mitsuharu]

Steps to reproduce:

1. $ emacs -Q &
2. Type the following expression and hit C-j in the *scratch* buffer.

  (save-excursion
    (goto-char (point-min))
    (insert-image (create-image "splash.png"))
    (insert ?\n))

3. Ditto.

   (pos-visible-in-window-p (point-min) nil t)

Result:

The expected one is (0 0), but the actual one is (608 188).  As far as
I tested, this happens at the first row (i.e., (window-start)) only
containing a single image.  If you remove (insert ?\n) in the first
expression, then the result is (0 0) as expected.

                                     YAMAMOTO Mitsuharu
                                mituharu@math.s.chiba-u.ac.jp

In GNU Emacs 24.3.92.1 (x86_64-apple-darwin13.2.0, GTK+ Version 3.12.2)
 of 2014-07-05 on YAMAMOTO-no-iMac.local
Repository revision: 117350 
stephen.berman@gmx.net-20140704190929-xpf743kwesgh2k4q
Windowing system distributor `The X.Org Foundation', version 11.0.11406000
Configured using:
 `configure --without-imagemagick LDFLAGS=-L/opt/local/lib
 CPPFLAGS=-I/opt/local/include'