## Change

Add a guard to the `disparate_dir` cleanup in `sync_instance` to 
prevent accidental deletion of the contract state directory when 
`DISPARATE_DIR` is not set.

## Background

The `disparate` directory feature was introduced in the beta devkit 
image to support multisig deployments. The cluster script assumes 
`DISPARATE_DIR` is always set, however older NPM packages (below 
v0.6.8) do not pass this environment variable, leaving `$disparate_dir` 
as an empty string.

With an empty `$disparate_dir` this line:
```bash
[ -d $contract_dir/contract_fs/seed/state/$disparate_dir ] && rm -r $contract_dir/contract_fs/seed/state/$disparate_dir
```

Evaluates to:
```bash
[ -d $contract_dir/contract_fs/seed/state/ ] && rm -r $contract_dir/contract_fs/seed/state/
```

Deleting the entire state directory immediately after the contract 
bundle is copied in.

## Change

Add a guard so the deletion only runs when `$disparate_dir` is 
actually set:
```bash
# Before
[ -d $contract_dir/contract_fs/seed/state/$disparate_dir ] && rm -r $contract_dir/contract_fs/seed/state/$disparate_dir

# After
[ -n "$disparate_dir" ] && [ -d $contract_dir/contract_fs/seed/state/$disparate_dir ] && rm -r $contract_dir/contract_fs/seed/state/$disparate_dir
```

## Notes

- NPM v0.6.8 correctly passes `DISPARATE_DIR=disparate` and is 
required for full beta devkit compatibility
- This guard is defensive programming to protect against the state 
directory being accidentally deleted if an older NPM package is used 
with the beta image
- For non-multisig deployments the disparate directory cleanup is 
skipped entirely which is the correct behaviour