fix crash abi parsing

key payable is nil and not defined for any functions

Author: nerzh

Sources/web3swift/EthereumABI/ABIParsing.swift

@@ -75,7 +75,7 @@ fileprivate func parseFunction(abiRecord:ABI.Record) throws -> ABI.Element.Funct
     let abiOutputs = outputs != nil ? outputs! : [ABI.Element.InOut]()
     let name = abiRecord.name != nil ? abiRecord.name! : ""
     let payable = abiRecord.stateMutability != nil ?
-        (abiRecord.stateMutability == "payable" || abiRecord.payable!) : false
+        (abiRecord.stateMutability == "payable" || abiRecord.payable ?? false) : false
     let constant = (abiRecord.constant == true || abiRecord.stateMutability == "view" || abiRecord.stateMutability == "pure")
     let functionElement = ABI.Element.Function(name: name, inputs: abiInputs, outputs: abiOutputs, constant: constant, payable: payable)
     return functionElement