forcepoint #34 survive missing autostyles

Change-Id: I742816297659d614e836a8d5e8965b1c55154719
Reviewed-on: https://gerrit.libreoffice.org/51892Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Stahl <Michael.Stahl@cib.de>
(cherry picked from commit 2446ae94)

sc/source/filter/xml/xmlcelli.cxx

@@ -365,6 +365,8 @@ void ScXMLTableRowCellContext::PushFormat(sal_Int32 nBegin, sal_Int32 nEnd, cons
     sal_Int32 nEntryCount = xMapper->GetEntryCount();
 
     SvXMLStylesContext* pAutoStyles = GetImport().GetAutoStyles();
+    if (!pAutoStyles)
+        return;
 
     // Style name for text span corresponds with the name of an automatic style.
     const XMLPropStyleContext* pStyle = dynamic_cast<const XMLPropStyleContext*>(