Some backstory:
- In [#45](https://github.com/vivaria/tja2fumen/pull/45), I reworked the
header parsing code to make sure every header value was correctly
identified.
- In [#46](https://github.com/vivaria/tja2fumen/pull/46), I changed how
the "branch point" header bytes were set by checking if a song contained
only drumroll branching conditions. This fixed drumroll-only songs like
BATTLE NO. 1, Shoutoku Taiko, etc.
However, I missed a corner case in #46 -- songs with `#BRANCHSTART
p,0,0` should still be considered "drumroll only". As well, I neglected
to consider the "percentage only" songs. So, I fixed the header bytes
there, too.
Then, to confirm that my changes do in fact produce correct headers, I
enabled the check for `branch_points` for (most) of the songs in the
test suite. The tests pass. :)
000125eb10