Fix for SVG group bounds erroneously including origin

Text(Span) nodes report a bounding box of [0,0,0,0], which caused
legitimate bounding boxes to be incorrectly expanded to encompass
the origin.

Added a check that each child has a non-zero bounding area before
using it to set or expand the group's bounding box.

Also corrected a broken file path to Cairo.h in the GoodMorning sample.

Happy Easter.