synth_name should be defined before reference

# What?

Likely due to my own messy Ruby api wrapping around live_loop function I got an error.

```
Error: Thread died: #<NameError: undefined local variable or method `synth_name' for #<SonicPiSpiderUser1:0x007f9f6b38fad8>>
```

I've not been able to replicate a just using SonicPi's core functions.

But this still looks like good hygiene since we make a reference to something that is not yet defined.