coverity#1158079 Unchecked dynamic_cast

Change-Id: Iab2c78af7dcf967ccdf5016266324c805856af0b

sw/source/core/txtnode/thints.cxx

@@ -1036,13 +1036,13 @@ SwTxtAttr* MakeTxtAttr(
     case RES_TXTATR_ANNOTATION:
         {
             pNew = new SwTxtAnnotationFld( static_cast<SwFmtFld &>(rNew), nStt, rDoc.IsClipBoard() );
-            if ( bIsCopy == COPY )
+            if (bIsCopy == COPY)
             {
                 // On copy of the annotation field do not keep the annotated text range by removing
                 // the relation to its annotation mark (relation established via annotation field's name).
                 // If the annotation mark is also copied, the relation and thus the annotated text range will be reestablished,
                 // when the annotation mark is created and inserted into the document.
-                const_cast<SwPostItField*>(dynamic_cast< const SwPostItField* >(pNew->GetFmtFld().GetField()))->SetName( OUString() );
+                const_cast<SwPostItField&>(dynamic_cast<const SwPostItField&>(*(pNew->GetFmtFld().GetField()))).SetName(OUString());
             }
         }
         break;