prevent double delete in calc's html parser, fdo#52107

Change-Id: I0a203a39697d3b12304e4b9dc99714cd7b2a008c
(cherry picked from commit 0d21d9dd)
Signed-off-by: Caolán McNamara <caolanm@redhat.com>

sc/source/filter/html/htmlpars.cxx

@@ -554,6 +554,7 @@ void ScHTMLLayoutParser::Adjust()
                 nCurRow = pS->nCurRow;
             }
             delete pS;
+            pS = NULL;
             nTab = pE->nTab;
             if (pTables)
             {