Make setPagePrintSettings() accept IsLandscape again

Regression from 80c35d97b9b3b60a091aae77de0ffef38cbf531a - invert
the check for boost::optional validity.

Change-Id: If4e041e1fe349c1fcb2c74b2e5780bf57300486f
Reviewed-on: https://gerrit.libreoffice.org/57309
Tested-by: Jenkins
Reviewed-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>
diff --git a/sw/source/uibase/uno/unotxdoc.cxx b/sw/source/uibase/uno/unotxdoc.cxx
index 31650d2..73e6927 100644
--- a/sw/source/uibase/uno/unotxdoc.cxx
+++ b/sw/source/uibase/uno/unotxdoc.cxx
@@ -1147,7 +1147,7 @@
        else if(sName == "IsLandscape")
        {
            auto b = o3tl::tryAccess<bool>(rVal);
            bException = bool(b);
            bException = !b;
            if (b)
            {
                aData.SetLandscape(*b);