Blind fix to TBs

Change-Id: I74165378255e3c844ee7f91a5d4eb09a573784bd
Reviewed-on: https://gerrit.libreoffice.org/30179
Reviewed-by: Julien Nabet <serval2412@yahoo.fr>
Tested-by: Julien Nabet <serval2412@yahoo.fr>

xmlsecurity/source/pdfio/pdfdocument.cxx

@@ -775,7 +775,7 @@ size_t PDFDocument::FindStartXRef(SvStream& rStream)
     // Find the "startxref" token, somewhere near the end of the document.
     std::vector<char> aBuf(1024);
     rStream.Seek(STREAM_SEEK_TO_END);
-    rStream.SeekRel(-1 * aBuf.size());
+    rStream.SeekRel(-1 * aBuf.capacity());
     size_t nBeforePeek = rStream.Tell();
     size_t nSize = rStream.ReadBytes(aBuf.data(), aBuf.size());
     rStream.Seek(nBeforePeek);