read_stb() btag mismatch

[Se7enLC]

If you call read_stb() more than ~128 times, there's a btag mismatch.

I was able to fix the problem by changing this line:
rstb_btag = (self.last_rstb_btag % 128) + 1
to
rstb_btag = (self.last_rstb_btag + 1) % 128