PDFBOX-2250: detect XRef streams to avoid false positives when searching for the XRef table/stream

git-svn-id: https://svn.apache.org/repos/asf/pdfbox/trunk@1615141 13f79535-47bb-0310-9956-ffa450edef68
PDFBOX-1915: extend radial shadings only if radius > 0

git-svn-id: https://svn.apache.org/repos/asf/pdfbox/trunk@1615145 13f79535-47bb-0310-9956-ffa450edef68
code reformatted using the template

git-svn-id: https://svn.apache.org/repos/asf/pdfbox/trunk@1615149 13f79535-47bb-0310-9956-ffa450edef68