coverity#735800 Dereference after null check

Change-Id: I025569d39ed4497938770b7df21fcef32cc83825
Reviewed-on: https://gerrit.libreoffice.org/55600Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

sc/source/filter/xml/xmlimprt.cxx

@@ -1806,7 +1806,7 @@ void SAL_CALL ScXMLImport::endDocument()
         }
 
         // There are rows with optimal height which need to be updated
-        if (!maRecalcRowRanges.empty())
+        if (pDoc && !maRecalcRowRanges.empty())
         {
             bool bLockHeight = pDoc->IsAdjustHeightLocked();
             if (bLockHeight)