bug#21413: Top of buffer hidden when toolbar hidden and frame height is large

[Devon Buchanan <devon@divinenephron.co.uk>]

Package: emacs
Version: 24.5.1

* Brief summary

When I turn tool-bar-mode off and make a frame taller than the 
height available on my screen the top of the buffer is hidden 
until I re-size the window.

* Steps to reproduce

Here are the steps to reproduce the problem using the NS build of 
emacs on OS X 10.10.4.

cat >> test-init.el <<EOF
(tool-bar-mode -1)
(setq default-frame-alist '((height . 100)))
EOF
open -a Emacs.app --args -Q -l ~/test-init.el

This opens a graphical emacs frame showing the *scratch* buffer. 
Neither the cursor is visible, nor is the text normally shown in 
the *scratch* buffer. Scrolling up will not make either of these 
visible. C-x C-f <some file name> RET will display the contents of 
that buffer with some or all of the lines at the start hidden.

The hidden sections of the buffer can be made visible by clicking 
and dragging on any edge of the window and resizing it.

* Expected behaviour

When I set the frame size to be taller than the screen will allow, I
expect the frame to occupy as much vertical space as possible without
the top of the buffer being hidden. This is the behaviour seen when
tool-bar-mode is on.