xmloff: avoid unhandled exception warning

Happened e.g. when copy&pasting editeng content in Impress tables,
document::XStorageBasedDocument is not implemented by SvxSimpleUnoModel,
so it's not exceptional that the queryInterface() for mxModel fails.

Change-Id: Iaed53941bb47ff8a0553896f18a553cf64e2224a
Reviewed-on: https://gerrit.libreoffice.org/49747Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Jenkins <ci@libreoffice.org>

xmloff/source/core/xmlimp.cxx

@@ -988,10 +988,9 @@ void SAL_CALL SvXMLImport::setTargetDocument( const uno::Reference< lang::XCompo
 
     try
     {
-        uno::Reference<document::XStorageBasedDocument> const xSBDoc(mxModel,
-                uno::UNO_QUERY_THROW);
-        uno::Reference<embed::XStorage> const xStor(
-                xSBDoc->getDocumentStorage());
+        uno::Reference<document::XStorageBasedDocument> const xSBDoc(mxModel, uno::UNO_QUERY);
+        uno::Reference<embed::XStorage> const xStor(xSBDoc.is() ? xSBDoc->getDocumentStorage()
+                                                                : nullptr);
         if (xStor.is())
         {
             mpImpl->mbIsOOoXML =