tdf#116851: some rtf files provide param with "-" for "edmins"

Change-Id: I2a2a189ee727a51aeef5601b39bb288d813fc8f3
Reviewed-on: https://gerrit.libreoffice.org/52610
Tested-by: Jenkins
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>
(cherry picked from commit c04c6c48)
Reviewed-on: https://gerrit.libreoffice.org/67708Reviewed-by: Julien Nabet <serval2412@yahoo.fr>
Reviewed-by: Xisco Faulí <xiscofauli@libreoffice.org>

writerfilter/source/rtftok/rtfdispatchvalue.cxx

@@ -1102,7 +1102,12 @@ RTFError RTFDocumentImpl::dispatchValue(RTFKeyword nKeyword, int nParam)
             break;
         case RTF_EDMINS:
             if (m_xDocumentProperties.is())
+            {
+                // tdf#116851 some RTF may be malformed
+                if (nParam < 0)
+                    nParam = -nParam;
                 m_xDocumentProperties->setEditingDuration(nParam);
+            }
             break;
         case RTF_NOFPAGES:
         case RTF_NOFWORDS: