coverity#1437957 Unchecked dynamic_cast

Change-Id: I1c1d699e585da5d758671422f8e438e5ac8b5b03
Reviewed-on: https://gerrit.libreoffice.org/57455
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

sw/qa/extras/ww8export/ww8export2.cxx

@@ -318,6 +318,7 @@ DECLARE_WW8EXPORT_TEST(testTdf70838, "tdf70838.odt")
 DECLARE_WW8EXPORT_TEST(testTdf70838b_verticalRotation, "tdf70838b_verticalRotation.odt")
 {
     SwXTextDocument* pTextDoc = dynamic_cast<SwXTextDocument *>(mxComponent.get());
+    CPPUNIT_ASSERT(pTextDoc);
     SwDoc* pDoc = pTextDoc->GetDocShell()->GetDoc();
     SdrPage* pPage = pDoc->getIDocumentDrawModelAccess().GetDrawModel()->GetPage(0);
     tools::Rectangle aGroupShape = pPage->GetObj(0)->GetSnapRect();