Fix issue 2567: NoneType check before raising exception

[SoulPancake]

Pull Request check-list

Please make sure to review and check all of these items:

• Does $ tox pass with this change (including linting)?
• Do the CI tests pass with this change (enable it first in your forked repo and wait for the github action build to finish)?
• Is the new or changed code fully tested?
• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?
• Is there an example added to the examples folder (if applicable)?
• Was the change added to CHANGES file?

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Description of change

The change made to the read_response function adds a check to ensure that self._buffer is not None before trying to call rewind on it. If self._buffer is None, the call to rewind is skipped and the exception is re-raised as normal.

This change is necessary to prevent the "AttributeError: 'NoneType' object has no attribute 'rewind'" error from being raised if an exception occurs during the call to self._read_response() and the connection to Redis has been closed. Without this check, the rewind call would raise an error because self._buffer would be None, and None does not have a rewind attribute.

[codecov-commenter]

Codecov Report

Base: 92.28% // Head: 92.00% // Decreases project coverage by -0.28% ⚠️

Coverage data is based on head (93a8fc4) compared to base (428d609).
Patch coverage: 100.00% of modified lines in pull request are covered.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2569      +/-   ##
==========================================
- Coverage   92.28%   92.00%   -0.28%     
==========================================
  Files         115      115              
  Lines       29660    29660              
==========================================
- Hits        27371    27289      -82     
- Misses       2289     2371      +82     

Impacted Files	Coverage Δ
redis/connection.py	86.69% <100.00%> (+0.01%)	⬆️
redis/retry.py	95.83% <0.00%> (-4.17%)	⬇️
redis/asyncio/retry.py	92.85% <0.00%> (-3.58%)	⬇️
tests/test_graph_utils/test_edge.py	94.59% <0.00%> (-2.71%)	⬇️
redis/client.py	86.52% <0.00%> (-2.68%)	⬇️
tests/test_pubsub.py	97.47% <0.00%> (-2.14%)	⬇️
tests/test_ssl.py	47.51% <0.00%> (-2.13%)	⬇️
tests/test_asyncio/test_graph.py	97.68% <0.00%> (-1.55%)	⬇️
tests/test_graph_utils/test_path.py	97.01% <0.00%> (-1.50%)	⬇️
tests/test_graph.py	90.28% <0.00%> (-1.29%)	⬇️
... and 13 more

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