regressions/ck_fifo: Require non-NULL stub node.

regressions/ck_fifo/validate/ck_fifo_mpmc.c

@@ -141,6 +141,8 @@ main(int argc, char *argv[])
 
 	ck_fifo_mpmc_init(&fifo, malloc(sizeof(ck_fifo_mpmc_entry_t)));
 	ck_fifo_mpmc_deinit(&fifo, &garbage);
+	if (garbage == NULL)
+		ck_error("ERROR: Expected non-NULL stub node on deinit.\n");
 	free(garbage);
 	ck_fifo_mpmc_init(&fifo, malloc(sizeof(ck_fifo_mpmc_entry_t)));
 

regressions/ck_fifo/validate/ck_fifo_spsc.c

@@ -160,6 +160,9 @@ main(int argc, char *argv[])
 
 		ck_fifo_spsc_init(fifo + i, malloc(sizeof(ck_fifo_spsc_entry_t)));
 		ck_fifo_spsc_deinit(fifo + i, &garbage);
+		if (garbage == NULL)
+			ck_error("ERROR: Expected non-NULL stub node on deinit.\n");
+
 		free(garbage);
 		ck_fifo_spsc_init(fifo + i, malloc(sizeof(ck_fifo_spsc_entry_t)));
 		r = pthread_create(thread + i, NULL, test, context + i);