cairo: Fix rectangles returned by StrokeExtents and FillExtents methods
cairo: Fix rectangles returned by StrokeExtents and FillExtents methods

The third and fourth parameters of the Rectangle constructor are width
and height, but cairo_stroke_extents and cairo_fill_extents give right
and bottom coordinates.

Signed-off-by: Bertrand Lorentz <eb7ac131ef7bff6d2ebccd6e5bf9a7cb6485cf2c@gmail.com>

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