Fix UnboundLocalError when reading byte_stream #122

Job	Run time
pre-commit	16s
mypy-strict	13s
build_wheel_and_sdist	18s
test_on_supported_Pythons (3.9, windows-latest)	50s
test_on_supported_Pythons (3.9, macos-latest)	58s
test_on_supported_Pythons (3.9, ubuntu-24.04)	34s
test_on_supported_Pythons (3.10, ubuntu-24.04)	29s
test_on_supported_Pythons (3.11, macos-latest)	1m 36s
test_on_supported_Pythons (3.10, windows-latest)	56s
test_on_supported_Pythons (3.11, ubuntu-24.04)	36s
test_on_supported_Pythons (3.13, macos-latest)	1m 41s
test_on_supported_Pythons (3.12, ubuntu-24.04)	34s
test_on_supported_Pythons (3.13, windows-latest)	51s
test_on_supported_Pythons (3.13, ubuntu-24.04)	35s
test_on_supported_Pythons (3.11, windows-latest)	51s
test_on_supported_Pythons (3.12, macos-latest)	1m 44s
test_on_supported_Pythons (3.14.0-beta.4, ubuntu-24.04)	42s
test_on_supported_Pythons (3.14.0-beta.4, macos-latest)	1m 59s
test_on_supported_Pythons (3.14.0-beta.4, windows-latest)	1m 36s
test_on_supported_Pythons (3.12, windows-latest)	1m 31s
test_on_supported_Pythons (3.10, macos-latest)	2m 0s
	20m 50s

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