Fix GetConstantValueAsByteArray() when o is s?byte
Fix GetConstantValueAsByteArray() when o is s?byte

jorik041/dnlib,kiootic/dnlib,Arthur2e5/dnlib,picrap/dnlib,ilkerhalil/dnlib,ZixiangBoy/dnlib,yck1509/dnlib,0xd4d/dnlib,modulexcite/dnlib