MT#55283 safeguard against incorrect usage

If keyspace notifications are not configured at all, bail with an error
when there is an attempt to add a new keyspace or remove one. We get a
segfault otherwise.

Closes #1902

Change-Id: Ie47cf5f7762792aabe38476739f0dcf9927787ce
(cherry picked from commit 6dbf098bc7)
(cherry picked from commit 96f5adaee1)

daemon/cli.c

@@ -1046,6 +1046,11 @@ static void cli_incoming_ksadd(str *instr, struct cli_writer *cw) {
 	unsigned long uint_keyspace_db;
 	char *endptr;
 
+	if (!rtpe_redis_notify) {
+		cw->cw_printf(cw, "Keyspace notification feature has not been configured.\n");
+		return;
+	}
+
 	if (str_shift(instr, 1)) {
 		cw->cw_printf(cw, "%s\n", "More parameters required.");
 		return;
@@ -1076,6 +1081,11 @@ static void cli_incoming_ksrm(str *instr, struct cli_writer *cw) {
 	unsigned long uint_keyspace_db;
 	char *endptr;
 
+	if (!rtpe_redis_notify) {
+		cw->cw_printf(cw, "Keyspace notification feature has not been configured.\n");
+		return;
+	}
+
 	if (str_shift(instr, 1)) {
 		cw->cw_printf(cw, "%s\n", "More parameters required.");
 		return;
@@ -1110,6 +1120,11 @@ static void cli_incoming_ksrm(str *instr, struct cli_writer *cw) {
 static void cli_incoming_kslist(str *instr, struct cli_writer *cw) {
 	GList *l;
 
+	if (!rtpe_redis_notify) {
+		cw->cw_printf(cw, "Keyspace notification feature has not been configured.\n");
+		return;
+	}
+
 	cw->cw_printf(cw,  "\nSubscribed-on keyspaces:\n");
 
 	rwlock_lock_r(&rtpe_config.keyspaces_lock);