fix: correct OS conditional for Windows paths

What was the problem/requirement? (What/Why)

When opening Cinema 4D on Mac with the AWS Deadline Cloud submitter installed, the following error appears:

Traceback (most recent call last):
  File "/Users/rickrams/c4dplugin/DeadlineCloud.pyp", line 25, in <module>
os.add_dll_directory(dll_path)
^^^^^^^^^^^^^^^^^^^^
AttributeError:module 'os' has no attribute 'add_dll_directory'

What was the solution? (How)

os.add_dll_directory(dll_path) is a Windows-only command. The conditional surrounding that code block was if "win" in sys.platform. The sys.platform value for Mac is darwin, which was unexpectedly True for the conditional.

Updated the conditional to if sys.platform in ["win32", "cygwin"]: to capture only the Windows OS.

What is the impact of this change?

Mac submissions are not yet officially supported with this change, but this is a step toward it.

How was this change tested?

Copied deadline.pyp into the C4D plugins folder. Re-ran the submitter.

Have you run the unit tests? Yes!

Did you run the "Job Bundle Output Tests"? If not, why not? If so, paste the test results here.

Yes

Was this change documented?

No, not required

Is this a breaking change?

No. This fixes a previously not working case.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

aws-deadline / deadline-cloud-for-cinema-4d