Fix signed/unsigned conversion bug for siphash functions
Fix signed/unsigned conversion bug for siphash functions

dipinhora/ponyc,cquinn/ponyc,CausalityLtd/ponyc,sgebbie/ponyc,cquinn/ponyc,kulibali/ponyc,ponylang/ponyc,dipinhora/ponyc,kulibali/ponyc,kulibali/ponyc,ponylang/ponyc,sgebbie/ponyc,sgebbie/ponyc,cquinn/ponyc,dipinhora/ponyc,jemc/ponyc,jemc/ponyc,sgebbie/ponyc,CausalityLtd/ponyc,jemc/ponyc,CausalityLtd/ponyc,cquinn/ponyc,kulibali/ponyc,ponylang/ponyc,sgebbie/ponyc