updated GetReflectiveLoaderOffset to handle PE32's and PE64's regardless of architecture

I updated GetReflectiveLoaderOffset to handle PE32's and PE64's regardless of the injector's architecture. I did this by adding boolean "is64" parameter to Rva2Offset. If is64 is true, PIMAGE_NT_NEADERS64 is used, otherwise PIMAGE_NT_NEADERS32 is used. This is useful when you have a DLL that doesn't match the architecture of the injecting code.