Check cluster_enabled in readwriteCommand just like readonlyCommand. (#9015)

src/cluster.c

@@ -5734,6 +5734,10 @@ void readonlyCommand(client *c) {
 
 /* The READWRITE command just clears the READONLY command state. */
 void readwriteCommand(client *c) {
+    if (server.cluster_enabled == 0) {
+        addReplyError(c,"This instance has cluster support disabled");
+        return;
+    }
     c->flags &= ~CLIENT_READONLY;
     addReply(c,shared.ok);
 }