[Audio] `disconnect` command should check if the user is actually in the VC

### What Red version are you using?

3.5.9

### Cog name

Audio

### Command name

disconnect

### What did you expect to happen?

- Just like the `summon` command - the `disconnect` cmd should **also** check if the user (who is invoking the command) actually is in the VC before letting them disconnect the bot from the VC - where it's already playing songs **along with** other humans.

### What actually happened?

It lets anyone **who is not in the VC**, run the command resulting in the bot getting disconnected from the VC, leading to an unpleasant experience.

### How can we reproduce this error?

1. Connect to a VC
2. Set the vote percentage to 0 by `audioset vote 0`
3. Summon the bot to join
4. Ask any user or `

mock` anyone to run `

disconnect`
Result - It should let that user x disconnect the bot without having to be there in the VC.
> The `summon` command ONLY works if you are in the VC - likewise, the disconnect should also work if the user is in the VC, regardless of the status of the `audioset vote`.

### Same result with or without the human. (Meaning if the bot is alone or with other users doesn't matter)

### Anything else?

N/A