Add a missing clear_current_lookup() call in recv_done()

The error code path handling the `ISC_R_CANCELED` code lacks a
`clear_current_lookup()` call, without which dig hangs indefinitely
when handling the error.

Add the missing call to account for all references of the lookup so
it can be destroyed.

bin/dig/dighost.c

@@ -3844,6 +3844,7 @@ recv_done(isc_nmhandle_t *handle, isc_result_t eresult, isc_region_t *region,
 		}
 		query_detach(&query);
 		lookup_detach(&l);
+		clear_current_lookup();
 		UNLOCK_LOOKUP;
 		return;
 	}