PDF-hul: more concise error message for PDF-HUL-80 "Invalid object number in cross-reference stream" (feature request)

[asciim0]

As for most PDF-HUL errors, the offset returned for PDF-HUL-80 "Invalid object number in cross-reference stream" sits at the end of of the stream object. This is not helpful at all when trying to trouble-shoot the error, as cross-reference streams can contain hundreds of object references. It would be much more helpful if JHOVE could report back which object number in the cross-reference stream is invalid.