bisect: check get_terms return at all call sites

Six callers of get_terms() silently discard its return value. When
get_terms fails (missing or truncated BISECT_TERMS file), the term
strings remain NULL or empty, causing confusing downstream
behavior: commands like "bisect next" or "bisect run" proceed with
empty term strings, producing nonsensical ref names (refs/bisect/
with no suffix) and misleading error messages.

Let's not discard the return value, but handle an error with the same
message `bisect_terms()` already uses when reading the terms failed.

Pointed out by Coverity.

There is one slight complication here: One caller _needs_ the return
value to indicate an error when the `BISECT_TERMS` file is absent, all
the other call sites are totally okay with a "missing" `BISECT_TERMS`
file. To address that, extend the function signature of `get_terms()` to
indicate which behavior the caller wants.

Assisted-by: Claude Opus 4.6
Helped-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

0 files changed, 0 insertions, 0 deletions