ofz: Null-deref

Change-Id: I5fefd9ba125c3769cdcb8a97f1a00a2aad5b21f4
Reviewed-on: https://gerrit.libreoffice.org/46369Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

sw/source/filter/html/swhtml.cxx

@@ -414,6 +414,8 @@ SwHTMLParser::~SwHTMLParser()
 #endif
 
     OSL_ENSURE(m_aContexts.empty(), "There are still contexts on the stack");
+    OSL_ENSURE(!m_nContextStMin, "There are protected contexts");
+    m_nContextStMin = 0;
     while (!m_aContexts.empty())
     {
         std::unique_ptr<HTMLAttrContext> xCntxt(PopContext());