u3: fix typo in u3s_sift_bytes() block conditionals
u3: fix typo in u3s_sift_bytes() block conditionals

ngzax/urbit,urbit/urbit,urbit/urbit,ngzax/urbit,ngzax/urbit,urbit/urbit,urbit/urbit,urbit/urbit,ngzax/urbit,ngzax/urbit,urbit/urbit,ngzax/urbit,urbit/urbit,ngzax/urbit