Fixed __repr__ call in EmptyStreamReader

[WindowGenerator]

What do these changes do?

Fixed an error when calling the __repr__ method on an EmptyStreamReader

Briefly about the solution:

Removes the problem associated with calling the __repr__ method on the super class. The problem comes from missing methods in the child class. So the decision was made to override the lower class's __repr__ method

Are there changes in behavior for the user?

The user will no longer get an error when calling __repr__ on an EmptyStreamReader

Related issue number

#6655

Checklist

• [x] I think the code is well written
• [x] Unit tests for the changes exist
• [x] Documentation reflects the changes
• [x] If you provide code modification, please add yourself to CONTRIBUTORS.txt
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• [x] Add a new news fragment into the CHANGES folder
  • name it <issue_id>.<type> for example (588.bugfix)
  • if you don't have an issue_id change it to the pr id after creating the pr
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    • .feature: Signifying a new feature.
    • .bugfix: Signifying a bug fix.
    • .doc: Signifying a documentation improvement.
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    • .misc: A ticket has been closed, but it is not of interest to users.
  • Make sure to use full sentences with correct case and punctuation, for example: "Fix issue with non-ascii contents in doctest text files."