Fix tooltip display with multiple monitors on windows.

Fix tooltip display with multiple monitors on windows.

On Windows the position of a window may be negative on a monitor to the
left of the primary display. A plus sign is used as the separator between
the width and height and the positional parts of the geometry so always
include the plus sign even for negative positions on this platform.

Signed-off-by: Pat Thoyts <patthoyts@users.sourceforge.net>