Passing quoted strings as arguments in REDIS_COMMAND does not work

When I try to put a string with a space into a key in Redis:

```
exten => s,1,NoOp(${REDIS_COMMAND(SET xxx "Hello world")})
```

... it emits an error:

```
[2016-08-17 06:34:54.771] ERROR[25919][C-00000049]: /root/src/func_redis/src/func_redis.c:425 function_redis_command: ERR wrong number of arguments for 'set' command
```
