tdf#130746: avoid nullptr dereference

Change-Id: I32979a23caffea844f1c8eac9f408b18f0768b62
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/90661
Tested-by: Jenkins
Reviewed-by: Justin Luth <justin_luth@sil.org>
(cherry picked from commit 81588ff2f0eb55576a5288778be2dfb5b4bc5e81)
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/90635
Reviewed-by: Michael Stahl <michael.stahl@cib.de>
diff --git a/sw/source/core/layout/frmtool.cxx b/sw/source/core/layout/frmtool.cxx
index d9b9c98c..7ece7bb 100644
--- a/sw/source/core/layout/frmtool.cxx
+++ b/sw/source/core/layout/frmtool.cxx
@@ -3434,9 +3434,9 @@ bool IsFrameInSameContext( const SwFrame *pInnerFrame, const SwFrame *pFrame )

static SwTwips lcl_CalcCellRstHeight( SwLayoutFrame *pCell )
{
    if ( pCell->Lower()->IsContentFrame() || pCell->Lower()->IsSctFrame() )
    SwFrame *pLow = pCell->Lower();
    if ( pLow && (pLow->IsContentFrame() || pLow->IsSctFrame()) )
    {
        SwFrame *pLow = pCell->Lower();
        long nHeight = 0, nFlyAdd = 0;
        do
        {
@@ -3463,7 +3463,6 @@ static SwTwips lcl_CalcCellRstHeight( SwLayoutFrame *pCell )
    else
    {
        long nRstHeight = 0;
        SwFrame *pLow = pCell->Lower();
        while (pLow && pLow->IsLayoutFrame())
        {
            nRstHeight += ::CalcRowRstHeight(static_cast<SwLayoutFrame*>(pLow));