Fix issues in cryptography_flutter #216

Job	Run time
Analyze (cryptography, beta)	29s
Analyze (jwk, beta)	31s
Analyze (cryptography, 3.3.0)	41s
Analyze (cryptography_flutter, 3.35.0)	1m 9s
Analyze (cryptography_flutter, beta)	44s
Analyze (cryptography_flutter/example, beta)	41s
Analyze (cryptography_test, 3.3.0)	41s
Analyze (jwk, 3.3.0)	42s
Analyze (cryptography_flutter_integration_test, 3.35.0)	57s
Analyze (cryptography_test, beta)	46s
Analyze (cryptography_flutter/example, 3.35.0)	1m 11s
Analyze (cryptography_flutter_integration_test, beta)	1m 6s
PANA	0s
Test	0s
PANA (cryptography_flutter)	1m 47s
	11m 25s

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