orchestrator fix: keep exchange object optional

[DropD]

The orchestrator decorator looks for an optional exchange object on the self argument of the decorated function. One helper function has code that doesn't check whether it's present before optionally using it.

This small PR puts that code inside an if condition, the same check used throughout the module to check for presence of the exchange object.

[github-actions]

Mandatory Tests

Please make sure you run these tests via comment before you merge!

• cscs-ci run default
• launch jenkins spack

Optional Tests

To run benchmarks you can use:

• cscs-ci run benchmark

To run tests and benchmarks with the DaCe backend you can use:

• cscs-ci run dace

In case your change might affect downstream icon-exclaim, please consider running

• launch jenkins icon

For more detailed information please look at CI in the EXCLAIM universe.

[DropD]

Would it be better to set all these keys to the default value (0)?

[kotsaloscv]

I would favour the if exchange_obj is not None and not isinstance(exchange_obj, decomposition.SingleNodeExchange) and set the pointers to 0.