Avoid a deadcode in catalog.c

For https://bugzilla.gnome.org/show_bug.cgi?id=703504
diff --git a/catalog.c b/catalog.c
index 8e34cd2..549e592 100644
--- a/catalog.c
+++ b/catalog.c
@@ -3550,8 +3550,8 @@
 		xmlGenericError(xmlGenericErrorContext,
 			"Setting catalog preference to SYSTEM\n");
 		break;
-	    case XML_CATA_PREFER_NONE:
-		break;
+	    default:
+		return(ret);
 	}
     }
     xmlCatalogDefaultPrefer = prefer;