PDFBOX-1915: fix BBox if coordinates are inverted; add BBox to shading 1,3,6,7 as suggested by Shaola Ren; drop empty BBox because of trouble with eci file

git-svn-id: https://svn.apache.org/repos/asf/pdfbox/trunk@1615722 13f79535-47bb-0310-9956-ffa450edef68