tdf#141816: fix a thinko

This must check if they are different, not the other way around

Change-Id: Id9b7a51f13d5d5c48077822ba18f0257b36ea226
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/114422
Tested-by: Jenkins
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>
diff --git a/svx/source/svdraw/svdundo.cxx b/svx/source/svdraw/svdundo.cxx
index 1805c06..2e81d8a 100644
--- a/svx/source/svdraw/svdundo.cxx
+++ b/svx/source/svdraw/svdundo.cxx
@@ -995,7 +995,7 @@ SdrUndoObjSetText::~SdrUndoObjSetText()
bool SdrUndoObjSetText::IsDifferent() const
{
    if (!pOldText || !pNewText)
        return !pOldText && !pNewText;
        return pOldText || pNewText;
    return !(*pOldText == *pNewText);
}