Check if we have status indicator

In other methods it's always checked, so presumably it might be absent.
In caller sites (like OOXMLFastContextHandler::endOfParagraph), it can't
(and shouldn't) be checked.

Change-Id: Ia2edf8b121cac15e6454bc6321d76517fcdf110f
Reviewed-on: https://gerrit.libreoffice.org/45951Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>

writerfilter/source/ooxml/OOXMLDocumentImpl.cxx

@@ -529,7 +529,8 @@ void OOXMLDocumentImpl::incrementProgress()
     if (mnProgressEndPos && mnProgressCurrentPos > (mnProgressLastPos + mnPercentSize) && mnProgressLastPos < mnProgressEndPos)
     {
         mnProgressLastPos = mnProgressCurrentPos;
-        mxStatusIndicator->setValue(mnProgressLastPos);
+        if (mxStatusIndicator.is())
+            mxStatusIndicator->setValue(mnProgressLastPos);
     }
 }