Fix `signMessage` failing for messages of certain lengths #1333

Job	Run time
Compile the UX-less version of the app on Nano S+ for performance tests	1m 28s
Compilation for X, S+, Stax and Flex (nanox, $NANOX_SDK)	1m 45s
Compilation for X, S+, Stax and Flex (nanosp, $NANOSP_SDK)	1m 46s
Compilation for X, S+, Stax and Flex (stax, $STAX_SDK)	2m 1s
Compilation for X, S+, Stax and Flex (flex, $FLEX_SDK)	1m 54s
Performance report	4m 22s
Tests with the JS library	1m 15s
Unit test	1m 32s
Tests with the Python library and legacy Bitcoin app	40s
Tests on mainnet (nanox)	26s
Tests for rust client library	1m 30s
Tests on mainnet (nanosp)	27s
Tests on mainnet (stax)	27s
Tests on mainnet (flex)	25s
	19m 58s

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