-Wmaybe-uninitialized in ScTable::CopyColFiltered

apply same initialization as in ScTable::CopyRowFiltered

Change-Id: I9e8de6eaae3b3ad9453e5c06a88cfa93766becd9
Reviewed-on: https://gerrit.libreoffice.org/11263Reviewed-by: Kohei Yoshida <libreoffice@kohei.us>
Tested-by: Kohei Yoshida <libreoffice@kohei.us>

sc/source/core/data/table5.cxx

@@ -837,7 +837,7 @@ void ScTable::CopyColFiltered(ScTable& rTable, SCCOL nStartCol, SCCOL nEndCol)
     SCCOL nCol = nStartCol;
     while (nCol <= nEndCol)
     {
-        SCCOL nLastCol;
+        SCCOL nLastCol = -1;
         bool bFiltered = rTable.ColFiltered(nCol, NULL, &nLastCol);
         if (nLastCol > nEndCol)
             nLastCol = nEndCol;