ProgressTask.GetPercentage() returns 100 when max value is 0

[FrankRay78]

fixes #981

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• I have commented on the issue above and discussed the intended changes
• A maintainer has signed off on the changes and the issue was assigned to me
• All newly added code is adequately covered by tests
• All existing tests are still running without errors
• The documentation was modified to reflect the changes OR no documentation changes are required.

Changes

ProgressTask.GetPercentage() returns 100 when max value is 0.

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