parse_elst's existing tests used segment_duration/media_time values that were
almost all zero or 0xFF bytes, so an index slip in the version-1 byte
extraction (reading a neighbouring byte, or one outside the entry entirely)
could return the same value by coincidence and the test wouldn't notice. Added
a fixture with every byte distinct and nonzero so any wrong offset is caught.
elst_offset_ticks's `empty_movie_ticks > 0` guard on the Some(mts) arm looked
like a pure optimisation, but shifting its boundary lets an
empty_movie_ticks == 0 call fall into the division instead of skipping it -
and a zero movie timescale (unreachable through from_reader, which filters it,
but not through this function's own contract) makes that division panic.
Pinned the boundary directly so the function stays safe on its own terms.
Documented nine further mutants as equivalent rather than chasing them:
media_edits/odd_rate and the None-arm's empty_movie_ticks check only gate a
tracing::warn!, never the returned offset, and parse_elst's b.len() < 8 vs
<= 8 boundary computes the same empty Vec either way once available = 0 is
worked through. Confirmed by re-running each mutation against the full test
suite.
Matthew Jackson
a8db2435cd