CORE-793: Fix memory leak in `BRWalletFeeForTxAmountWithFeePerKb`
CORE-793: Fix memory leak in `BRWalletFeeForTxAmountWithFeePerKb`

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