sapyb to return even if out is not None

[paskino]

Changes in this pull request

With CIL TomographicImaging/CIL#1742 sapyb needs to return even if the output is pre-allocated

Testing performed

Reintroduced test_SIRF.py from CIL.
SyneRBI/SIRF-SuperBuild#897

Related issues

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• I have performed a self-review of my code
• I have added docstrings/doxygen in line with the guidance in the developer guide
• I have implemented unit tests that cover any new or modified functionality
• The code builds and runs on my machine
• CHANGES.md has been updated with any functionality change

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• The content of this Pull Request (the Contribution) is intentionally submitted for inclusion in SIRF (the Work) under the terms and conditions of the Apache-2.0 License.