fix negative int32 #3
fix negative int32 #3

vgatto/protobuf-swift,DouglasHeriot/protobuf-swift,iguchunhui/protobuf-swift,hejunbinlan/protobuf-swift,hejunbinlan/protobuf-swift,vgatto/protobuf-swift,alexeyxo/protobuf-swift,Navdy/protobuf-swift,Navdy/protobuf-swift,wearezeta/protobuf-swift,wearezeta/protobuf-swift,NachoSoto/protobuf-swift,mwoytowich/protobuf-swift,alexeyxo/protobuf-swift,DouglasHeriot/protobuf-swift,NachoSoto/protobuf-swift,getcircle/protobuf-swift,iguchunhui/protobuf-swift,mwoytowich/protobuf-swift,getcircle/protobuf-swift,NachoSoto/protobuf-swift,wearezeta/protobuf-swift,getcircle/protobuf-swift,DouglasHeriot/protobuf-swift,hejunbinlan/protobuf-swift,vgatto/protobuf-swift,iguchunhui/protobuf-swift,NachoSoto/protobuf-swift,hejunbinlan/protobuf-swift,Navdy/protobuf-swift,DouglasHeriot/protobuf-swift,alexeyxo/protobuf-swift,mwoytowich/protobuf-swift,Navdy/protobuf-swift,alexeyxo/protobuf-swift,mwoytowich/protobuf-swift,getcircle/protobuf-swift,vgatto/protobuf-swift,iguchunhui/protobuf-swift,wearezeta/protobuf-swift