PDFBOX-2250: skip empty xref table followed by trailer, leave call that will create empty instead of null curXrefTrailerObj when xref table is empty (merged from trunk)

git-svn-id: https://svn.apache.org/repos/asf/pdfbox/branches/1.8@1633186 13f79535-47bb-0310-9956-ffa450edef68