fdo#83354: Chart is truncated - moved down outside the margins of the object

Handle the case when the content height is unitialized (0).
When content height is 0 it means there is no content (so
we don't need to calculate adjustment) or the content height is
uninitialized which leads to wrong calculated value.

Regression from:
cb19042f4395c97d123a27c6960d5e30d666c010

Change-Id: I45570a71f0597847820ce77e8dcec4a5b0c6785d
diff --git a/sw/source/core/layout/fly.cxx b/sw/source/core/layout/fly.cxx
index 05ed4c9..80773d3 100644
--- a/sw/source/core/layout/fly.cxx
+++ b/sw/source/core/layout/fly.cxx
@@ -1732,9 +1732,15 @@ void SwFlyFrm::MakeContentPos( const SwBorderAttrs &rAttrs )
        Point aNewContentPos;
        aNewContentPos = Prt().Pos();
        const SdrTextVertAdjust nAdjust = GetFmt()->GetTextVertAdjust().GetValue();

        if( nAdjust != SDRTEXTVERTADJUST_TOP )
        {
            SwTwips nDiff = (Prt().*fnRect->fnGetHeight)() - CalcContentHeight(&rAttrs, nMinHeight, nUL);
            const SwTwips nContentHeight = CalcContentHeight(&rAttrs, nMinHeight, nUL);
            SwTwips nDiff = 0;

            if( nContentHeight != 0)
                nDiff = (Prt().*fnRect->fnGetHeight)() - nContentHeight;

            if( nDiff > 0 )
            {
                if( nAdjust == SDRTEXTVERTADJUST_CENTER )