New version throws client missing
**Describe the bug**

Getting `client missing` when attempting to perform actions.

Version 0.0.219 (latest)

This is new since I updated to the lastest version and it's fixed after a restart. what I noticed is that when I try to restart my homebridge it throws the following error, I'm sure that because the `client` is undefined. is there something I can do to get more debugging information?

```
[3/29/2020, 2:02:12 PM] TypeError: Cannot read property 'methodCall' of undefined     at HomeMaticRPC.stop (/usr/local/lib/node_modules/homebridge-homematic/HomeMaticRPC.js:315:15)     at process.<anonymous> (/usr/local/lib/node_modules/homebridge-homematic/index.js:151:19)     at process.emit (events.js:215:7)
``` 

**Which Homematic Device or Service the bug is about**

all

**To Reproduce**
Steps to reproduce the behavior:

Not sure yet, after a while the `client` is gone. a restart is fixing it for now

**Actual behaviour**
Actions are not performed and a `client missing` error is thrown in the console


**Expected behavior**
Actions should be performed

I'm happy to help with debugging.

cheers
ben
