When evaluating (set-frame-position nil 0 0), emacs frame moves to
top-left of the screen, but there is a gap between the left edge of the
screen and the emacs frame.
The displayed position of 'emacs -g +0+0' is same as the above.

The attached image is the result of the commands below.
    runemacs -Q -D -T emacs --geometry +0+0
    runemacs -Q -D -T emacs --geometry -0+0
    runemacs -Q -D -T emacs --geometry +0-0
    runemacs -Q -D -T emacs --geometry -0-0