narrow the assert condition further down

Change-Id: Ia9b1db652b2f15b66b89b51038d16fb0da6ffb6d
diff --git a/sc/source/core/data/postit.cxx b/sc/source/core/data/postit.cxx
index 9bd602b..2acc07a 100644
--- a/sc/source/core/data/postit.cxx
+++ b/sc/source/core/data/postit.cxx
@@ -1097,10 +1097,11 @@ void ScPostIt::RemoveCaption()
    }
    // Either the caption object is gone or, because of Undo or clipboard is
    // held in at least two instances, or only one instance in Undo because the
    // original sheet was deleted, or the Undo document is just destroyed
    // which leaves us with one reference.
    // original sheet in this document is just deleted, or the Undo document is
    // just destroyed which leaves us with one reference.
    // Let's detect other use cases..
    assert(!maNoteData.mxCaption || maNoteData.mxCaption.getRefs() >= 2 || !mrDoc.IsUndo() || mrDoc.IsInDtorClear());
    assert(!maNoteData.mxCaption || maNoteData.mxCaption.getRefs() >= 2 ||
            (!mrDoc.IsUndo() && !mrDoc.IsClipboard()) || (mrDoc.IsUndo() && mrDoc.IsInDtorClear()));
    maNoteData.mxCaption.reset(nullptr);
}