[cookie_manager] Fix `FileSystemException` when saving redirect cookies without a proper `host` #578

Job	Run time
Check formatting (dio)	14s
Check formatting (example)	12s
Check formatting (example_flutter_app)	9s
Check formatting (plugins/cookie_manager)	12s
Check formatting (plugins/http2_adapter)	14s
Check formatting (plugins/native_dio_adapter)	12s
Analyze Flutter libraries (example_flutter_app)	1m 26s
Analyze Flutter libraries (plugins/native_dio_adapter)	1m 20s
Analyze Dart-only libraries (dio)	17s
Analyze Dart-only libraries (example)	16s
Analyze Dart-only libraries (plugins/cookie_manager)	19s
Analyze Dart-only libraries (plugins/http2_adapter)	15s
Run unit tests with Flutter plugins (min, plugins/native_dio_adapter)	32s
Run unit tests with Flutter plugins (stable, plugins/native_dio_adapter)	44s
Run unit tests with Flutter plugins (beta, plugins/native_dio_adapter)	1m 46s
Run unit tests with dio (2.15.0, vm)	1m 14s
Run unit tests with dio (2.15.0, chrome)	3m 32s
Run unit tests with dio (stable, vm)	1m 8s
Run unit tests with dio (stable, chrome)	3m 59s
Run unit tests with dio (beta, vm)	1m 9s
Run unit tests with dio (beta, chrome)	3m 30s
Run unit tests with plugins (2.15.0, plugins/cookie_manager)	25s
Run unit tests with plugins (2.15.0, plugins/http2_adapter)	59s
Run unit tests with plugins (stable, plugins/cookie_manager)	25s
Run unit tests with plugins (stable, plugins/http2_adapter)	1m 8s
Run unit tests with plugins (beta, plugins/cookie_manager)	25s
Run unit tests with plugins (beta, plugins/http2_adapter)	1m 3s
	27m 5s

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