Failer to boot into Safe Mode

```python
import microcontroller
microcontroller.on_next_reset(microcontroller.RunMode.BOOTLOADER)
microcontroller.reset()
```
works as expected but
```python
import microcontroller
microcontroller.on_next_reset(microcontroller.RunMode.SAFE_MODE)
microcontroller.reset()
```

Does not enter safe mode. I was going to use it like "else statement" boots to safe_mode stopping code.