mingw32 build: python_modules/marshal: use unsigned for for_loop index variable
mingw32 build: python_modules/marshal: use unsigned for for_loop index variable

fgouget/spice-protocol,vdiot/spice-protocol,SPICE/spice-protocol,SPICE/spice-protocol,SPICE/spice-protocol,vdiot/spice-protocol,fgouget/spice-protocol,vdiot/spice-protocol,fgouget/spice-protocol