Missing CAP_CHOWN results in files.log.ftl to be empty

[yubiuser]

Actual behavior / bug

When CAP_CHOWN is missing, FTL will set files.log.ftl empty. It stays empty even after re-adding the cap.
This can be reproduced easily in docker with adding

    cap_drop:
      - CAP_CHOWN

Expected behavior

files.log.ftl should stay untouched

[DL6ER]

Thank you for the report. I was able to track this down: the root cause is in init_FTL_log(): When CAP_CHOWN is missing and fopen() fails on the log file, the code sets config.files.log.ftl.v.s = NULL to fall back to syslog. However, this corrupts the in-memory config value unintentionally.

Shortly after (in main.c:), readFTLconf() calls initConfig() which intentionally skips resetting files.log.ftl (to preserve the early-parsed value), and then readFTLtoml() fails to restore it from the TOML file because the NULL v.s short-circuits the strcmp check in readTOMLvalue(). When the config is rewritten to disk, printTOMLstring() converts the NULL to "", permanently blanking the setting.

The fix uses a separate static bool ftl_log_available flag in log.c to control syslog fallback, instead of modifying the config value. This is not particularly pretty but it easily preserves the configured path so it survives both the TOML rewrite and subsequent restarts.