Tighten up the check decoding maps with enum values.
Tighten up the check decoding maps with enum values.

cburrows/swift-protobuf,tbkka/swift-protobuf,thomasvl/swift-protobuf,thomasvl/swift-protobuf,apple/swift-protobuf,tbkka/swift-protobuf,apple/swift-protobuf,allevato/swift-protobuf,cburrows/swift-protobuf,apple/swift-protobuf,allevato/swift-protobuf,tbkka/swift-protobuf,thomasvl/swift-protobuf,cburrows/swift-protobuf,tbkka/swift-protobuf,tbkka/swift-protobuf,apple/swift-protobuf,cburrows/swift-protobuf,thomasvl/swift-protobuf,allevato/swift-protobuf,thomasvl/swift-protobuf,thomasvl/swift-protobuf,apple/swift-protobuf,apple/swift-protobuf,apple/swift-protobuf,cburrows/swift-protobuf,tbkka/swift-protobuf,cburrows/swift-protobuf,tbkka/swift-protobuf,allevato/swift-protobuf,allevato/swift-protobuf,allevato/swift-protobuf,cburrows/swift-protobuf,thomasvl/swift-protobuf,allevato/swift-protobuf