not necessary to open read/write to extract document metadata

Change-Id: Idf1bfbac1adc083f6d697d19ca41110f765955e9
Reviewed-on: https://gerrit.libreoffice.org/16171Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Andras Timar <andras.timar@collabora.com>
(cherry picked from commit 30c4467d)

sfx2/source/doc/SfxDocumentMetaData.cxx

@@ -2012,6 +2012,7 @@ SfxDocumentMetaData::loadFromMedium(const OUString & URL,
     // if we have an URL parameter, it replaces the one in the media descriptor
     if (!URL.isEmpty()) {
         md[ utl::MediaDescriptor::PROP_URL() ] <<= URL;
+        md[ utl::MediaDescriptor::PROP_READONLY() ] <<= true;
     }
     if (md.addInputStream()) {
         md[ utl::MediaDescriptor::PROP_INPUTSTREAM() ] >>= xIn;