avoid crash when no table grid is given

The document may contain just <w:tblGrid/> and <w:tblW w:w="0" w:type="auto"/> .
It appears we do not handle the auto width properly at all, but at least don't crash.

Change-Id: Ibdc9d1ad69c13456acd347a151ec8739bcb98855

writerfilter/source/dmapper/DomainMapperTableManager.cxx

@@ -584,6 +584,10 @@ void DomainMapperTableManager::endOfRowAction()
         text::TableColumnSeparator* pSeparators = aSeparators.getArray();
         sal_Int16 nSum = 0;
         sal_uInt32 nPos = 0;
+        // Avoid divide by zero (if there's no grid, position using cell widths).
+        if( nFullWidthRelative == 0 )
+            for (sal_uInt32 i = 0; i < pCellWidths->size(); ++i)
+                nFullWidthRelative += (*pCellWidths.get())[i];
 
         for (sal_uInt32 i = 0; i < pCellWidths->size() - 1; ++i)
         {