tdf#110993 - Corrected spline calculation

The algorithm in Numerical Recipies in C, 2nd edition in Section 3.3,
page 166 states a division rather than a multiplication.

Change-Id: I2530c506bc48726539e3de99016892e50d6bb87e
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/115465
Tested-by: Jenkins
Reviewed-by: Andreas Heinisch <andreas.heinisch@yahoo.de>
(cherry picked from commit e6442b39836f9856aa7b87d1a840158f0cb7d9c4)
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/117974
Reviewed-by: Xisco Fauli <xiscofauli@libreoffice.org>
diff --git a/chart2/source/view/charttypes/Splines.cxx b/chart2/source/view/charttypes/Splines.cxx
index 774d5fc..338179b 100644
--- a/chart2/source/view/charttypes/Splines.cxx
+++ b/chart2/source/view/charttypes/Splines.cxx
@@ -198,7 +198,7 @@ void lcl_SplineCalculation::Calculate()
            ( m_fYpN - ( m_aPoints[ n ].second - m_aPoints[ n - 1 ].second ) / xDiff );
    }

    m_aSecDerivY[ n ] = ( un - qn * u[ n - 1 ] ) * ( qn * m_aSecDerivY[ n - 1 ] + 1.0 );
    m_aSecDerivY[ n ] = ( un - qn * u[ n - 1 ] ) / ( qn * m_aSecDerivY[ n - 1 ] + 1.0 );

    // note: the algorithm in [1] iterates from n-1 to 0, but as size_type
    // may be (usually is) an unsigned type, we can not write k >= 0, as this