Edits refuse to leave anything beyond MAX_COORD (doc_sane checks the
artboards, the guides, the ruler origin and the objects an edit touches),
but the native loader didn't check them. A file with one object, artboard,
guide or ruler origin out there opened without a warning, and then every
move failed with "result would exceed the canvas", in-range objects
included; saving kept it that way.
Document::drop_beyond_canvas removes objects whose geometric bounds aren't
finite or reach past MAX_COORD (a layer or non-clipping group keeps its
children within it), artboards with their artboard guides, and guides out
there, and puts the ruler origin back at the origin. load_file runs it
after the depth limit and reports what it did with the other load notes; a
file whose artboards all lie beyond the canvas is refused.
