coverity#1430102 Division by zero

Change-Id: Iae44c89c4af70e3e5b19137ee08ca566c7a04fb7
Reviewed-on: https://gerrit.libreoffice.org/54141Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

sw/source/ui/misc/pggrid.cxx

@@ -405,9 +405,11 @@ IMPL_LINK(SwTextGridPage, CharorLineChangedHdl, SpinField&, rField, void)
     }
     else//in normal mode
     {
-        if(m_pLinesPerPageNF == &rField)
+        if (m_pLinesPerPageNF == &rField)
         {
-            long nHeight = static_cast< sal_Int32 >(m_aPageSize.Height() / m_pLinesPerPageNF->GetValue());
+            auto nValue = m_pLinesPerPageNF->GetValue();
+            assert(nValue && "div-by-zero");
+            long nHeight = static_cast< sal_Int32 >(m_aPageSize.Height() / nValue);
             m_pTextSizeMF->SetValue(m_pTextSizeMF->Normalize(nHeight), FUNIT_TWIP);
             m_pRubySizeMF->SetValue(0, FUNIT_TWIP);
             SetLinesOrCharsRanges( *m_pLinesRangeFT , m_pLinesPerPageNF->GetMax() );