pdf export: make FontIdentifier comparison strict weak ordering.

VS Runtime Library debug assertion failed "Expression: invalid
operator<" when exporting attachment of tdf#98879 to pdf.
The document uses both vertical and vertical fonts.

Change-Id: I4a2c519c539c28515cac876298be820cad8b9014
Reviewed-on: https://gerrit.libreoffice.org/33082Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

vcl/source/gdi/pdffontcache.hxx

@@ -45,8 +45,9 @@ namespace vcl
                 std::type_info *pType = rRight.m_typeFontFace;
 
                 return m_nFontId < rRight.m_nFontId ||
-                       m_typeFontFace->before( *pType ) ||
-                       m_bVertical < rRight.m_bVertical;
+                       ( m_nFontId == rRight.m_nFontId &&
+                       ( m_typeFontFace->before( *pType ) ||
+                       ( *m_typeFontFace == *pType && m_bVertical < rRight.m_bVertical ) ) );
             }
         };
         struct FontData