CORE-655: Properly protect `System.systemMapping` during *all* modifications.
CORE-655: Properly protect `System.systemMapping` during *all* modifications.

breadwallet/breadwallet-core,breadwallet/breadwallet-core,breadwallet/breadwallet-core,breadwallet/breadwallet-core,breadwallet/breadwallet-core,breadwallet/breadwallet-core