PDFBOX-1497 : if the deviceN array doesn't have Attributes, the getAttributes returns null

git-svn-id: https://svn.apache.org/repos/asf/pdfbox/trunk@1436553 13f79535-47bb-0310-9956-ffa450edef68
- added getter for TYPE
- replaces some Strings with COSNames
Merge remote-tracking branch 'upstream/trunk' into trunk