Don't pass a negative value to __redisAsyncCommand if redisFormatSdsCommandArgv fails

async.c

@@ -676,6 +676,8 @@ int redisAsyncCommandArgv(redisAsyncContext *ac, redisCallbackFn *fn, void *priv
     int len;
     int status;
     len = redisFormatSdsCommandArgv(&cmd,argc,argv,argvlen);
+    if (len < 0)
+        return REDIS_ERR;
     status = __redisAsyncCommand(ac,fn,privdata,cmd,len);
     sdsfree(cmd);
     return status;