IMAGE: changed the return type for dxf_image_read().

Signed-off-by: bert <bert.timmerman@xs4all.nl>
changed the return type for dxf_insert_read().

Signed-off-by: bert <bert.timmerman@xs4all.nl>
LAYER: changed the return type for dxf_layer_read().

Signed-off-by: bert <bert.timmerman@xs4all.nl>