forcepoint#40 null deref

presumably since

commit 0098bee7
Date:   Thu Sep 21 06:48:09 2017 +0200

    tdf#112501: Pivot table: popupbuttons are placed on wrong cells

Change-Id: I5413c0ba06fca25cb22256a20ef9640767dd9e50
Reviewed-on: https://gerrit.libreoffice.org/54970Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Christian Lohmaier <lohmaier+LibreOffice@googlemail.com>
(cherry picked from commit 69c5be9b)
(cherry picked from commit 47f090e2)

sc/source/filter/excel/xipivot.cxx

@@ -1569,13 +1569,13 @@ void XclImpPivotTable::ApplyMergeFlags(const ScRange& rOutRange, const ScDPSaveD
         itr    = aFieldBtns.begin();
         itrEnd = aFieldBtns.end();
         vector<const ScDPSaveDimension*>::const_iterator itDim = aFieldDims.begin();
-        for (; itr != itrEnd; ++itr, ++itDim)
+        for (; itr != itrEnd; ++itr)
         {
             ScMF nMFlag = ScMF::Button;
-            const ScDPSaveDimension* pDim = *itDim;
-            if (pDim->HasInvisibleMember())
+            const ScDPSaveDimension* pDim = itDim != aFieldDims.end() ? *itDim++ : nullptr;
+            if (pDim && pDim->HasInvisibleMember())
                 nMFlag |= ScMF::HiddenMember;
-            if (!pDim->IsDataLayout())
+            if (!pDim || !pDim->IsDataLayout())
                 nMFlag |= ScMF::ButtonPopup;
             rDoc.ApplyFlagsTab(itr->Col(), itr->Row(), itr->Col(), itr->Row(), itr->Tab(), nMFlag);
         }