better fix (i.e. one which actually works) for VC++ warnings in release build

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@14544 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/helpbest.cpp

@@ -94,8 +94,9 @@ wxString wxBestHelpController::GetValidFilename( const wxString& filename ) cons
         default:
             // we CAN'T get here
             wxFAIL_MSG( wxT("wxBestHelpController: Must call Initialize, first!") );
-            return wxEmptyString;
     }
+
+    return wxEmptyString;
 }
 
 #endif