fdo#74507: Ensure that we have non-null pointer to ScColumn.

Else it would cause a null pointer dereferencing when "precision as shown"
option is set.

Change-Id: Ie8d2fdb916b575fff7e0217c45c18a2c799577cb

sc/source/core/data/dociter.cxx

@@ -170,7 +170,7 @@ bool ScValueIterator::GetThis(double& rValue, sal_uInt16& rErr)
                 bNextColumn = true;
         }
 
-        ScColumn* pCol = NULL;
+        ScColumn* pCol = &(pDoc->maTabs[mnTab])->aCol[mnCol];
         if (bNextColumn)
         {
             // Find the next available column.