fftester: empty tabbox protection

Change-Id: I56b0845205d6968355b3327721bf9ca0930903e1
(cherry picked from commit b3533883)
Reviewed-on: https://gerrit.libreoffice.org/28424Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: David Tardon <dtardon@redhat.com>

sw/source/core/docnode/ndtbl.cxx

@@ -1329,6 +1329,8 @@ lcl_SetTableBoxWidths2(SwTable & rTable, size_t const nMaxBoxes,
     for (size_t nTmpLine = 0; nTmpLine < rLines.size(); ++nTmpLine)
     {
         SwTableBoxes & rBoxes = rLines[nTmpLine]->GetTabBoxes();
+        if (rBoxes.empty())
+            continue;
         size_t const nMissing = nMaxBoxes - rBoxes.size();
         if (nMissing)
         {