热点规则配置不生效问题 | ParamFlowRule does not take effect

## Issue Description

BUG：添加热点规则后，不生效

### Describe what happened (or what feature you want)
热点规则没有起到熔断效果
当对某一资源名添加热点规则设置为
参数索引：0
单机阈值：1
统计窗口时长：1秒
进行测试，发现1秒内狂点连接并携带索引为0的参数，并没有起到熔断
### Describe what you expected to happen
希望可以起到熔断效果，保证呈现正常效果

### How to reproduce it (as minimally and precisely as possible)

1. 设置参数索引：0
2. 设置单机阈值：1
3. 设置统计窗口时长：1秒
4. 1秒内请求10次路由并携带参数0

### Tell us your environment
windows环境，java1.8，maven3.6，sentinel版本：1.8.6，sentinel-dashboard：1.8.6

### Anything else we need to know?

Reproduce the issue with Sentinel 1.8.6 and sentinel-dashboard 1.8.6 using the stated Windows, Java 8, and Maven 3.6 environment. Start by tracing how ParamFlowRule uses parameter index 0, a threshold of 1, and a one-second window for the requested route. Done means repeated requests carrying parameter 0 trigger the expected circuit-breaking behavior.

Written by the indexing model from the issue text.